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(CNN) -- The United Nations predicted a jump in the number of Syrian refugees and appealed for nearly half a billion dollars to help meet their needs as a major rebel offensive in the country's largest city, Aleppo, got under way Thursday.
Here are the latest developments in the Syrian civil war.
Refugee numbers could skyrocket as displaced live in squalor
The number of Syrian refugees in neighboring countries could reach 700,000 by the end of the year, the U.N. refugee agency said Thursday. That figure would represent about 3% of the country's population.
How refugees are living in dirt on the Turkish border
Members of the Free Syrian Army react as they fire a homemade rocket toward regime forces in Deir al-Zor on Sunday, June 16. Tensions in Syria flared in March 2011 during the onset of the Arab Spring, escalating into an ongoing civil war. View the most compelling images taken since the start of the conflict.
Syrian civil war in photos
Civil war 'intense as ever' in Homs
Three cities, one war, thousands dead
The agency gave the number in an announcement seeking $487.9 million to support Syrian refugees. The United Nations is leading 52 humanitarian organizations in the effort.
The funds would go toward the soaring number of refugees flocking to Jordan, Lebanon, Iraq and Turkey.
In March, the United Nations predicted that as many as 100,000 Syrians could become refugees by the end of the year, but that figure was surpassed in July. The new projection indicates the worsening situation on the ground.
There are 294,000 Syrian refugees registered or awaiting registration in neighboring countries, the agency said.
In northern Syria, people fleeing the war endure filthy conditions at an impromptu encampment. Thousands of Syrians were being turned back at the border with Turkey, which said its facilities were overfilled.
Children were scavenging in surrounding fields for twigs to use for cooking fires as women line up next to a water tank that was pumping milky-looking water.
Many of the residents told stories of having fled towns that were pummeled by rockets and airstrikes.
Jihadists claim responsibility for bombing
A jihadi paramilitary group formed during the Syrian uprising claimed responsibility for an attack Wednesday on the Syrian army headquarters in Damascus.
In a statement posted on jihadi Web forums, the Al Nusra Front vowed to launch more attacks to "liberate the people of Syria from the tyrant," a reference to President Bashar al-Assad.
It said its fighters started the attack by detonating a suicide car bomb outside the building, and then had four attackers posing as security guards infiltrate the compound.
The state-run Syrian Arab News Agency said four Syrian guards were "martyred" and 14 other people, including civilians and members of the military, were wounded in two "terrorist bombings" Wednesday targeting the General Staff building in Damascus.
"Decisive battle for Aleppo"
In a telephone interview, Free Syrian Army Col. Abdu Jabar Agadi said rebel troops had launched an offensive he called, "The Decisive Battle for Aleppo."
"I cannot provide any more details of the battle out of tactical concern for troops but, God willing, we will be victorious soon," he said.
Abdulla Yasin, a spokesman for FSA Aleppo, said thousands of FSA fighters were involved in the offensive.
"The FSA will push forward across multiple fronts to make major gains in Aleppo," he said. "This battle will never ever end until we have victory in Aleppo."
He said government forces appear to be "at a weak point and stretched thin."
The government-run SANA news agency said "terrorists" had fired on citizens protesting against terrorist groups in Aleppo.
"A unit of the armed forces targeted a gathering for terrorists in al-Bazeh Square in the old city of Aleppo killing a number of them," it said. "Army forces also, targeted two terrorist dens in al-kallasa and killed them all."
At least 115 people died in attacks nationwide Thursday, the LCC said.
On Wednesday, the single-day death toll hit 343, the highest since the unrest started last year, an opposition group said.
Witness: Scores killed in 'massacre' near Damascus
"The regime is escalating the violence at every possible opportunity, and it is proof that it is determined to crush the revolution by any means necessary," said Rafif Jouejati, an LCC spokeswoman.
The second-deadliest day was August 25, when 330 people were killed, according to the opposition group.
Syria said authorities "stormed a terrorists' hideout" in Hama and seized weapons, including Russian rifles.
"On Wednesday evening, authorities destroyed a number of cars for the terrorists which were loaded with weapons and ammunition near al-Zohouri Mosque in al-Qseir city in Homs province," SANA reported.
A pipeline carrying crude oil exploded before dawn Thursday, creating a large fire, and unknown men kidnapped the station's manager, the opposition Syrian Observatory for Human Rights said.
SANA said that "an armed terrorist group on Wednesday evening detonated a crude oil transfer pipeline" and that another such group had "kidnapped engineer Ayman Shaqqouf, director of Tal al-Baiyda oil station."
Background
The Syrian crisis broke out in March 2011 after unarmed protesters, inspired by the success of popular uprisings in Egypt and Tunisia, took to the streets demanding political reform and an end to four decades of rule by the Assad family.
The movement devolved into an armed conflict after a brutal and continuing crackdown by regime forces.
Since the unrest began, more than 30,000 people have been killed, the opposition Syrian Observatory for Human Rights said.
More: Syrian artist's comic take on suffering
CNN's Hamdi Alkhshali and Ivan Watson contributed to this report.
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Syrian rebels leave their position in the northwestern town of Maaret al-Numan on Thursday, June 13. The White House said that the Syrian government has crossed a "red line" with its use of chemical weapons and announced it would start arming the rebels.
Forces loyal to Syrian President Bashar al-Assad are seen near Qusayr on Thursday, May 30.
Syrian rebels take position in a house during clashes with regime forces in the old city of Aleppo on May 22.
Syrian army soldiers take control of the village of Western Dumayna north of the rebel-held city of Qusayr on Monday, May 13. Syrian troops captured three villages in Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP.
Rebel fighters fire at government forces in the northern Syrian city of Aleppo on Sunday, May 12.
Searchers use a flashlight as they look for survivors among the rubble created by what activists say was a missile attack from the Syrian regime, in Raqqa province, Syria, on April 25.
A Kurdish fighter from the "Popular Protection Units" (YPG) takes position inside a building in the majority-Kurdish Sheikh Maqsood area of Aleppo, on Apri. 21.
People walk past destroyed houses in the northern Syrian town of Azaz on Sunday, April 21.
Free Syrian Army fighters take positions prior to an offensive against government forces in the Khan al-Assal area, near Aleppo on Saturday, April 20.
Men inspect damage at a house destroyed in an airstrike in Aleppo on April 15.
Syrian and Kurdish rebel fighters walk in the Sheikh Maqsud district of Aleppo on April 14.
A female rebel monitors the movement of Syrian government forces in Aleppo's Sheikh Maqsud neighborhood on April 11.
A rebel runs to avoid sniper fire from Syrian government forces in Aleppo on Thursday, April 11.
Syrian rebels observe the movement of Syrian government forces around Al-Kendi hospital in Aleppo on Wednesday, April 10.
Rescue teams and security forces check out the scene of a deadly car bomb explosion in Damascus on April 8.
The fighting has taken a toll on buildings in Aleppo's Saladin district, seen here on April 8.
A Syrian rebel runs for cover in Deir ez-Zor on April 2.
A rebel checks for snipers across the street toward the Citadel in Aleppo, Syria, on Saturday, March 30, in this photo taken by iReporter Lee Harper.
A Free Syrian fighter mourns the death of a friend in Aleppo on March 30, in this photo taken by iReporter Lee Harper.
A Syrian opposition fighter runs for cover from Syrian army snipers in Aleppo on Wednesday, March 27.
A Syrian girl covers her face to protect herself from fumes as a street covered with uncollected garbage is fumigated in Aleppo on Sunday, March 24.
A Syrian man and his family drive past damaged buildings in Maarat al-Numan, on Wednesday, March 20.
Syrians carry the body of a Syrian army soldier during a funeral ceremony in Idlib province on Tuesday, March 19.
Syrian rebels take position in Aleppo, the largest city in the country, on March 11.
Syrian men search for their relatives amongst the bodies of civilians executed and dumped in the Quweiq River on March 11.
A Free Syrian Army fighter looks back as smoke rises during fighting between rebel fighters and forces loyal to Syria's President Bashar al-Assad on the outskirts of Aleppo on Saturday, March 2.
Residents read Shaam News newspapers published by the Free Syrian Army in Aleppo on March 2.
A member of the Free Syrian Army reacts to the death of a comrade who was killed in fighting, at Bustan al Qasr cemetery in Aleppo on Friday, March 1.
A rebel fighter throws a home-made grenade at Syrian government forces in Aleppo on February 16.
A member of the Free Syrian Army stands with his weapon as he looks at a rainbow in Aleppo on February 16.
A Syrian woman looks through a bus window in Aleppo on February 14.
Free Syrian Army fighters walk through a dust-filled stairwell in Damascus on February 7.
A Syrian rebel gestures at comrades from inside a broken armored personnel carrier in Al-Yaqubia on February 6.
A rebel fighter throws a hand grenade inside a Syrian Army base in Damascus on February 3.
People stand in the dust of a building destroyed in an airstrike in Aleppo, Syria on February 3.
Free Syrian Army fighters run as they enter a Syrian Army base during heavy fighting in the Arabeen neighborhood of Damascus on February 3.
An unexploded mortar shell fired by the Syrian Army sits lodged in the ground in Damascus on January 25.
Fighters from Fateh al Sham unit of the Free Syrian Army fire on Syrian Army soldiers at a check point in Damascus on January 20.
A Free Syrian Army fighter walks between buildings damaged during Syrian Air Force strikes in Damascus on January 19.
A Syrian rebel fighter tries to locate a government jet fighter in Aleppo on January 18.
Syrian rebels launch a missile near the Abu Baker brigade in Albab on January 16.
A Syrian boy walks near rubbish next to tents at a refugee camp near the northern city of Azaz on the Syria-Turkey border, on January 8.
Syrians look for survivors amid the rubble of a building targeted by a missile in Aleppo on January 7.
A father reacts after hearing of a shelling by forces loyal to Syria's President Bashar al-Assad in Aleppo on January 3.
A patient smokes a cigarette at Dar Al-Ajaza psychiatric hospital in Aleppo on December 18, 2012. The psychiatric ward, housing around 60 patients, has lacked the means to function properly since fighting broke out there in July.
Syrians mourn a fallen rebel fighter at a rebel base in the al-Fardos area of Aleppo on December 8.
Members of Liwa (Brigade) Salahadin, a Kurdish military unit fighting alongside rebel fighters, monitor the area in the besieged district of Karmel al-Jabl in Aleppo on December 6.
A member of Liwa Salahadin aims at a regime fighter in the besieged district of Karmel al-Jabl in Aleppo on December 6.
Two young boys sit underneath a washline in a refugee camp on the border between Syria and Turkey near Azaz on December 5.
The bodies of three children, who were allegedly killed in a mortar shell attack that landed close to a bakery in Aleppo, on December 2, are laid out for identification by family members at a makeshift hospital at an undisclosed location of the city.
Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo on December 1 as fighting continues through the night.
Damaged houses in Aleppo are seen after an airstrike on November 29.
A Syrian rebel mourns the death of a comrade in Maraat al-Numan on November 20.
Syrians protesters stand on Assad's portrait during an anti-regime demonstration in Aleppo on November 16.
A Syrian rebel takes cover during fighting against Syrian government forces in Aleppo on November 15.
Syrian opposition fighter Bazel Araj, 19, sleeps next to his pistol in Aleppo on November 11.
A rebel fighter fires at a Syrian government position in Aleppo on November 6.
A Syrian rebel leaps over debris left in the street while running across a "sniper alley" near the Salahudeen district in Aleppo on November 4.
Rebels hold their position in the midst of a battle on November 3 in Aleppo.
A man cries while being treated in a local hospital in a rebel-controlled area of Aleppo on October 31.
A man is treated for wounds after a government jet attacked the Karm al-Aser neighborhood in eastern Aleppo on October 31.
A Syrian rebel interrogates a handcuffed and blindfolded man suspected of being a pro-regime militiaman in Aleppo on October 26.
Smoke rises from a fuel station following a mortar attack as Syrian women walk on a rainy day in the Arqub neighborhood of Aleppo on October 25.
A Syrian rebel fires at an army position in the Karm al-Jabal district of Aleppo on October 22.
A wounded Syrian boy sits on the back of a truck carrying victims and wounded people to a hospital following an attack by regime forces in Aleppo on October 21.
A man lies on the ground after being shot by a sniper for a second time as he waits to be rescued by members of the Al-Baraa Bin Malek Battalion, part of the Free Syria Army's Al-Fatah brigade, in Aleppo on October 20.
Syrian army soldiers run for cover during clashes with rebel fighters at Karam al-Jabal neighborhood of Aleppo on October 20.
Smoke rises after a Syrian Air Force fighter jet fired missiles at the suburbs of the northern province of Idlib on October 16.
A Syrian opposition fighter stands near a post in Aleppo on October 11.
A Syrian man mourns the death of his father, who was killed during a government attack in Aleppo on October 10.
A rebel fighter is carried by his friends and laid on a gurney to be treated for gunshot wounds sustained during heavy battles with government forces in Aleppo on October 1.
Syrian rebels help a wounded comrade to an Aleppo hospital after he was injured in a Syrian army strike on September 18.
Free Syria Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16.
A Syrian man carrying grocery bags tries to dodge sniper fire as he runs through an alley near a checkpoint manned by the Free Syria Army in Aleppo on September 14.
A woman walks past a destroyed building in Aleppo on September 13.
Free Syrian Army fighters battle during street fighting against Syrian army soldiers in Aleppo on September 8.
A Syrian man wounded by shelling sits on a chair outside a closed shop in Aleppo on September 4.
A woman sits in her wheelchair next to her house, damaged by a Syrian air raid, near Homs on August 26.
Members of the Free Syrian Army clash with Syrian army soliders in Aleppo's Saif al-Dawla district on August 22.
A man mourns in front of a field hospital on August 21 in Aleppo.
Wounded civilians wait in a field hospital after an air strike on August 21 in Aleppo.
People pray during the funeral of a Free Syrian Army fighter, Amar Ali Amero, on August 21.
A man cries near the graves of his two children killed during a recent Syrian airstrike in Azaz on August 20.
A Syrian woman holds her dead baby as she screams upon seeing her husband's body being covered following an airstrike by regime forces on the town of Azaz on August 15.
A Syrian rebel runs in a street of Selehattin during an attack on the municipal building on July 23.
Syrian rebels hunt for snipers after attacking the municipality building in the city center of Selehattin on July 23.
Members of the Free Syrian Army's Mugaweer (commandos) Brigade pay their respects in a cemetery on May 12 in Qusayr.
Syrian rebels take position near Qusayr on May 10.
A Free Syrian Army member takes cover in underground caves in Sarmin on April 9.
Rebels prepare to engage government tanks that advanced into Saraquib on April 9.
Men say prayers during a ceremony in Binnish on April 9.
A young boy plays with a toy gun in Binnish on April 9.
A Free Syrian Army rebel mounts his horse in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, a year after the uprising began.
Syrian refugees walk across a field before crossing into Turkey on March 14.
A rebel takes position in Al-Qsair on January 27.
A protester in Homs throws a tear gas bomb back towards security forces, on December 27, 2011.
A man stands under a giant Syrian flag outside the Umayyad Mosque in Damascus on December 24, 2011.
A member of the Free Syrian Army looks out over a valley in the village of Ain al-Baida on December 15, 2011.
Members of the Free Syrian Army stand in an valley near the village of Ain al-Baida, close to the Turkish border, on December 15, 2011.
Displaced Syrian refugees walk through an orchard adjacent to Syria's northern border with Turkey on June 14, 2011, near Khirbet al-Jouz.
A Syrian man holds up a portrait of President Bashar al-Assad during a rally to show support for the president in Damascus on April 30, 2011.
Syrians rally to show their support for President Bashar al-Assad in Damascus on April 30, 2011.
A screen grab from YouTube shows thick smoke rising above as Syrian anti-government protesters demonstrate in Moaret Al-Noman on April 29, 2011.
A screen grab from YouTube shows Syrian anti-government protesters run for cover from tear gas fired by security forces in Damascus on April 29, 2011, during the "Day of Rage" demonstrations called by activists to put pressure on al-Assad.
Syrians wave their national flag and hold portraits of al-Assad during a rally to show their support for their leader in Damascus on March 29, 2011.
A woman sits by the hospital bed of a man allegedly injured when an armed group seized rooftops in Latakia on March 27, 2011, and opened fire at passers-by, citizens and security forces personnel according to official sources.
Syrian protesters chant slogans in support of al-Assad during a rally in Damascus on March 25, 2011.
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