(CNN) -- The United Nations' secretary-general slammed Syrian President Bashar al-Assad's regime Saturday, saying the government "has manifestly failed to protect civilians" and the fighting "is destroying the country."
"The situation in Syria is rapidly deteriorating," Ban Ki-moon said during a visit to Croatia. "As fighting intensifies across the country, including in the capital, the suffering gets worse. I am deeply distressed by the rising death toll, and the growing number of people who have been forced to flee their homes within the country and across the borders."
Battles are raging in Damascus and a range of hotspots across the nation, and unrest is flaring in the Kurdish region. A fierce crackdown launched by the Syrian government against protesters starting in March 2011 has morphed into a nationwide uprising against the regime.
The government resolved to take on its foes after a bombing Wednesday killed four members of al-Assad's inner circle and government. The dead included al-Assad's brother-in-law, his defense minister, a security adviser, and the head of the national security bureau.
Damascus is now largely isolated by checkpoints and tanks, witnesses said Saturday. But tanks, artillery and mortars pummeled the neighborhood of Barzeh. Opposition groups said medicine is running out and residents are appealing for help.
"When I went outside to get some food and medicine I noticed that the streets are almost empty," an activist named Lena said from the Mazzeh neighborhood on the west side of the city. "Only those who have an urgent need to be outside like me were walking on the street. ... No one can really go in or out of the city without passing a checkpoint."
At least 13 of 96 people killed across the country Saturday were from Damascus and the Damascus suburbs, the opposition Local Coordination Committees of Syria said. Other deaths occurred in the provinces of Idlib, Homs, Daraa, Deir Ezzor, and Aleppo.
After largely sitting on the sidelines of the Syrian revolution, political groups from Syria's Kurdish minority in the northeastern region appear to have moved decisively to claim control of several Kurdish-populated towns.
The Kurdish Coordination Committee, an opposition group, said the towns of Amouda and Qobani are under the control of a group called the Free Kurdish Army. Opposition groups told Syrian officials and security forces to withdraw from the town.
The towns are near the Turkish border. The Free Kurdish Army, formed from the political Democratic Union Party, has historic links to the Kurdistan Workers' Party, or PKK.
The PKK, regarded as a terrorist organization by Turkey and the United States, has been fighting the Turkish government for Kurdish autonomy. There was no immediate comment from Turkey about the development. Turkey has been critical of the al-Assad regime and is hosting Syrian opposition groups and sheltering thousands of Syrian refugees.
Rebels are working to wrest control of Qamishli, the largest of the Kurdish cities, from the government. Clashes between Free Syrian Army rebels and regime forces were taking place near the city's Central Prison, the LCC said.
The Kurdish Coordination Committee reported fighting between Kurdish rebels and security forces in Malikiye, located east of Qamishli across from the Turkish border city of Cizre.
CNN cannot independently confirm reports of violence because the government restricts access by foreign journalists.
Rebel fighters seeking control of the country's northern and eastern borders reported success on the border with Iraq. A senior Iraqi army official in Anbar province said eight crossing points are in rebel hands. The official did not want to be named because he is not authorized to talk to the media.
Iraqi security forces have increased their military and security presence at the border in Anbar, the official said.
Late Friday, Iraqi Prime Minister Nuri al-Maliki urged Iraqis in Syria to return home.
"Given the difficult security conditions experienced by our brothers and our sons in Syria, we call on them -- men, women and children -- to return to their country. ... And we tell them to please come back home, the place of your safety and honor. We will forgive all those who ... do not have blood on their hands so everyone can live in peace and security," he said in a statement.
Travelers along the Syrian-Turkish border told CNN they saw rebels controlling border points.
Military defections have plagued the Syrian regime. An official from the Turkish Foreign Ministry confirmed to CNN that two brigadier generals from Syria arrived in Turkey Friday night and one arrived the night before. He said about two dozen Syrian generals have fled to Turkey.
The United Nations estimates more than 10,000 people have been killed since the crisis began more than 16 months ago. But Rupert Colville, a spokesman for the office of the U.N. high commissioner for human rights, said the United Nations hasn't been giving out overall death toll numbers since December "because it became impossible to verify the numbers in any meaningful way."
Opposition groups tracking deaths have issued higher tolls. The LCC, for example, estimates that more than 16,000 have died.
Diplomats have yet to come up with a plan to stop what is now being called a civil war.
The Arab League is expected to meet Sunday in Doha, Qatar, to discuss Syria, according to a senior Arab League official. The secretary-general will meet first with a five-member committee handling Syria before presenting a proposal to the wider group, also Sunday night, the official said.
The U.N. Security Council adopted a resolution renewing its Syrian observer mission for 30 days Friday. Diplomats said that if the violence engulfing Syria doesn't recede enough for the observers to do their work, the U.N. Supervision Mission in Syria, known as UNSMIS, will be withdrawn.
The mission's job is to monitor U.N. and Arab League joint special envoy Kofi Annan's six-point peace plan that never got off the ground. It recently suspended its regular patrols because of the escalating violence.
Lt. Gen. Babacar Gaye, U.N. military adviser for peacekeeping operations, has taken over temporary command of the supervision mission. Gaye, from Senegal, replaces Maj. Gen. Robert Mood of Norway, whose tour of duty ended Friday, the mission's website said.
Ban said Saturday that he is sending Herve Ladsous, the U.N. under-secretary-general for peacekeeping operations, "to assess the situation" and Gaye to lead the supervision mission "in this critical phase."
"The extension of UNSMIS mandate for only 30 days is a strong signal that the onus is -- above all -- on the parties, and with the Syrian government in the first place, who must stop the killing and the use of heavy weapons against population centers. All armed operations must end," Ban said.
"This is their basic responsibility. A meaningful and inclusive political process cannot take root as long as violence, fear and intimidation continue to rage across the country.
Ban said he is working closely with Annan.
"We continue to push for a peaceful solution," he said. "The situation is fluid and unpredictable, but the path to peace is clear. There must be an end to killing and human rights violations, and a rapid move towards a peaceful, Syrian-led political transition and political dialogue. Urgent and visible steps towards a credible transition would constitute an alternative to the violence."
CNN's Mohamed Fadel Fahmy, Ivan Watson, Yesim Comert, Amir Ahmed, Saad Abedine, Mohammed Tawfeeq and Joe Sterling contributed to this report.