(CNN) -- Syrian President Bashar al-Assad offered vague promises of reform and clear threats against protesters Monday, as he addressed his nation and the rest of the world, whose leaders called for swift changes, some saying he had passed the point of no return.
Months of protests have left more than 1,100 dead, according to human rights activists. But the extent of the carnage is not clear. U.S. Secretary of State Hillary Clinton said last week that nearly 1,300 Syrians had been killed and thousands more jailed since protests began.
The Syrian leader said he was "working on getting the military back to their barracks as soon as possible" but also warned the government would "work on tracking down everyone who shed blood or plotted in shedding the blood of the Syrian people, and we will hold them accountable."
He raised the possibility of amending the country's constitution and referred to the need for a "national dialogue," but made clear his government would not engage in one-on-one talks with the opposition.
"It is not a dialogue of the opposition with the government ... but it should be a dialogue that will include all fabrics of the Syrian society," he said in the speech, his third to the country in three months.
Al-Assad blamed armed gangs and conspiracies for the violence that has gripped the country, saying the unrest has tarnished the country's image and weakened its security.
"There are some who are distorting the image of the Syrian nation abroad, and they wanted to open the gates and even called for foreign intervention. They tried to weaken the national political position," he said in the speech to an enthusiastic audience at Damascus University.
"There are those who are killing in the name of religion and want to spread chaos under the pretext of religion," he said, referring to conspiracies as "germs" that cannot be "exterminated."
The speech was met with demonstrations in a number of Syrian towns and cities, opponents of the government said.
Videos posted on YouTube suggested there were protests in Damascus, Hama, Homs and other cities.
It was not possible to confirm when or where the scenes were filmed, but one showed a sign reading, "If we are all germs, are you the head of all germs?"
Malath Aumran, a human rights activist, said security forces attacked people at Aleppo University and arrested more than 50 students, some of whom were protesting against the Assad speech. CNN could not confirm the report.
The European Union on Monday condemned "in the strongest possible terms the worsening violence in Syria."
"The Syrian authorities must stop the violence, put an immediate end to arbitrary arrests and intimidations, release all those arrested in connection with protests, as well as other political prisoners who remain in detention despite the recent amnesty," it said.
French Foreign Minister Alain Juppe was unmoved by al-Assad's speech. "I believe he has reached the point of no return," Juppe said in Luxembourg, according to a ministry spokeswoman. "And in any case it is not the speech that was made today that is going to change the context."
Israeli Defense Minister Ehud Barak assessed the speech in similar terms: "It's my personal judgment that Bashar Assad crossed the point of no return towards his demise."
Shortly after the president's speech, Syria's state news agency announced the discovery of a mass grave in the restive border town of Jisr al-Shugur, where thousands of people have fled a Syrian military offensive.
The grave contained "bodies of the martyrs of security forces and police who were assassinated by the armed terrorist gangs," state TV alleged.
The state news agency said Monday a large cache of weapons had been discovered in the town near the Turkish border.
Al-Assad called in his speech for refugees from the town to go back home.
"I urge them to return to their homes that they have left as soon as they can and disregard those who are spreading these baseless rumors that the security forces will mistreat them," the president said. "The military is there for the sake of their security, the safety of the citizens and their cities."
Al-Assad has faced growing criticism from leaders in the United States, Europe and elsewhere over his government's violent clampdown on demonstrators.
In Moscow, Russian Foreign Minister Sergey Lavrov called on al-Assad to move quickly to institute reforms and called on the opposition to negotiate with the government.
"Russia will do everything it can to prevent the situation in Syria from developing along the Libyan scenario," Lavrov said, referring to the North African country where NATO air forces have been bombing forces loyal to leader Moammar Gadhafi since March, when the U.N. Security Council passed a resolution authorizing the use of force to protect unarmed protesters.
In an interview published Monday by the Financial Times, Russian President Dmitry Medvedev went a step further, saying Russia would veto any resolution in the United Nations Security Council on Syria that might be similar to the Libyan one.
Medvedev said he felt "very sorry" for al-Assad and had urged him to move forward with reforms and enter into dialogue with all political forces. "But what I am not prepared to support is a resolution similar to Resolution 1973 on Libya," he said. "I am deeply convinced that a rather good resolution has been turned into a piece of paper which covers a senseless military operation."
In Washington, State Department spokeswoman Victoria Nuland noted that al-Assad "spends a lot of time blaming foreign instigators rather than appreciating that his own people are simply disgusted by a regime that supports itself through repression, corruption and fear."
She said the U.S. ambassador to Syria, Robert Ford, was en route to northern Syria's border with Turkey "so that he can take his own account of what is happening up there." Syria has closed that border, she said.
There is growing evidence that Iran, which has long considered Syria almost a satellite state, is stepping up its efforts to influence what is happening inside the country, U.S. officials said Monday, but they did not make that evidence public.
One U.S. official told CNN that electronic intercepts show Iranian Revolutionary Guard Corps involvement in Syria during the recent violence that points to increased cooperation.
The official expressed the belief that an increased number of Iranian personnel are moving in and out of Damascus and potentially assisting in training Syrian forces and facilitating weapons flows, which the official said "continue unchecked."
Another U.S. official accused Iran of having supplied Syria with riot-control gear.
At the same time, the first official told CNN, the Iranian Revolutionary Guard Corps is hedging its bets, supporting other regime "players" so that, if al-Assad were to fall from power, Iran would still have influence in the country.
The State Department has increasingly criticized Iranian involvement, but has not been specific. "Syria has taken a page out of Iran's playbook, if you will, in employing a lot of the same tactics that we saw Iran use following the 2009 election," State Department spokesman Mark Toner said last week in a reference to Tehran's violent crackdown on peaceful demonstrators. "But in terms of evidence, it's difficult for me to talk about a lot of that evidence from the podium."
On Monday, President Barack Obama called Turkish Prime Minister Recep Tayyip Erdogan to discuss regional developments, the White House press secretary said in a statement. "The leaders agreed that the Syrian government must end the use of violence now and promptly enact meaningful reforms that respect the democratic aspirations of the Syrian people," it said.
The Turkish government has said 10,639 Syrians crossed the border prior to the closure, more than half of them children. About 3,000 more were huddled on the Syrian border near Badama, witness Jameel Saib told CNN Saturday.
Refugees are living in four camps managed by Turkey and the Turkish Red Crescent, the U.N. High Commissioner for Refugees reported Saturday.
In London, Foreign Secretary William Hague called al-Assad's speech "disappointing and unconvincing" and called for "an immediate end to violence by Syrian security forces, the release of all political prisoners, an end to the torture and abuse of those who remain in detention and access given to international humanitarian agencies."
During his address, al-Assad said he had met a number of Syrians who voiced legitimate demands that the government improve the economy and increase personal freedoms.
He promised to "reform what has been damaged," though he said it would take time.
"For us, the reform process is an absolute conviction that will be in the best interest of the nation and the citizens. We just can't jump into the unknown. We are working on building the way to our future," al-Assad said.
CNN has not been allowed into Syria to cover the unrest and draws from social media and interviews with witnesses on the ground there to inform its reporting.
CNN's Barbara Starr, Saad Abedine, Saskya Vandoorne, Maxim Tkachenko, Salma Abdelaziz, Tim Lister, Jenifer Fenton, Per Nyberg and Kamal Ghattas contributed to this report.