An image grab taken from a video uploaded by Ugarit News, a Syrian opposition web channel, shows Syrian anti-government protesters holding the current (top) and former Syrian flags during a demonstration in the central city of Hama on June 17, 2011. (-/AFP/ GETTY IMAGES / UGARIT NEWS)

Tens of thousands of Syrians poured onto the streets of cities around the country Friday to press their demand for the resignation of President Bashar al-Assad, amid signs that his government is starting to crack under the strain of more than three months of unrest and growing international pressure.

In a now-weekly ritual since demonstrations erupted in mid-March, Syrians spilled out of mosques after Friday prayers chanting slogans calling for the government’s downfall. Just as predictably, Syrian security forces opened fire on them, killing at least 18 people and wounding dozens more, according to the Local Coordination Committees, a group that organizes and monitors protests.

The shootings made it clear that the Syrian government is not abandoning its strategy of relying on force to quell the dissent, despite scant evidence that it is working. Sizable protests took place this week in several suburbs of Damascus and in Aleppo, Syria's economic capital, where one protester was shot dead in the city’s first such fatality. Tens of thousands took to the streets in the central city of Hama, where the government appears to have given up trying to assert control.

In recent days, however, the regime has signaled that it is starting to recognize that it will have to do more than simply shoot people if it is to survive. Reports of small but significant defections from the army; indications that even the elite force on which the government relies to suppress the dissent is stretched; and, perhaps most crucially, a rift in Syria’s once-close relationship with Turkey have combined to give the government jitters for the first time.

“They’re definitely panicking,” said Andrew J. Tabler of the Washington Institute for Near East Policy. “The protests are just spreading, and they’re growing bigger, and whatever the Assad regime is doing, it isn’t working.”

One sign of the mood came Thursday, when Rami Makhlouf, Syria’s most powerful businessman, announced he was quitting his companies to devote his life to charity. Though he held no government position, as Assad’s cousin and childhood friend Makhlouf was regarded as a core member of the regime’s inner circle. He controlled a large chunk of the economy through his holdings and acted as manager for the Assad family’s finances.

Opposition figures dismissed the gesture as cosmetic and said it would not affect their demand that Assad step down. Far from appeasing protesters, the move will only energize the opposition, said Beirut-based activist Rami Nakhle.

“This will give them more confidence because it shows all their efforts are making a difference,” he said.

More significantly, Assad is expected to make a televised address to the nation in the coming days, his first direct address to the people and only his third speech since the crisis began. He has not spoken publicly since mid-April, has not been seen since mid-May and for several days last week refused to take phone calls from U.N. Secretary General Ban Ki-moon. Speculation mounted that his control is slipping as his powerful younger brother, Maher al-Assad, takes the lead in suppressing the unrest in his role as commander of the elite 4th Armored Division.

Others interpret Assad’s absence as just another indicator of the government’s conviction that it can weather the storm by relying on force and ignoring both domestic and international opinion. No one appears to expect Assad to make major concessions, and after more than 1,200 deaths and 10,000 detentions, for most protesters the time for those has long since passed.

The Obama administration has seen no response to pressure exerted on Assad, a senior administration official told reporters in Washington. Friday’s violence was a repetition of the “appalling repression . . . of the last few weeks,” the official said, adding that Assad is “putting his country on the path of a pariah state.”

Another official said the administration was examining “whether there are grounds here for charges related to war crimes and whether referrals on that are appropriate.”

“We’re also looking at additional economic steps, and one in particular has to do with the oil and gas sector in Syria,” the second official said.

But the government appears to have been seriously rattled by the abrupt turnaround by Turkey’s Prime Minister Recep Tayyip Erdogan, formerly one of Syria’s most reliable regional allies and a personal friend of Assad’s. After thousands of Syrian refugees surged into Turkey to escape the escalating violence, Erdogan condemned the government’s “barbarity,” prompting Assad to dispatch a senior envoy to Ankara for talks.

Perhaps most alarming for the Assad regime are reports in the Turkish press that Turkey is considering setting up a buffer zone for Syrian refugees along the countries’ mutual border. Turkish officials have dismissed the reports, and analysts say it is unlikely Turkey would want to take such an active role for fear of being drawn into military intervention in Syria.

But there is little doubt the opposition would welcome some form of haven, and if the crisis in Syria worsens and hundreds of thousands of refugees start crossing into Turkey, it cannot be ruled out, analysts say. The opposition could use such a haven to organize and supply activists in Syria and nurture a nascent alternative government, along the lines of the opposition to Moammar Gaddafi in eastern Libya.

“This is the nightmare for the Syrian regime, to have a Syrian Benghazi,” said Ausama Monajed, an opposition activist based in London.

That may explain why the fiercest crackdowns against the protest movement have come in border cities, initially with the dispatch of tanks into the southern town of Daraa near the Jordanian border in April and, most recently, in the northern town of Jisr al-Shughour, near the northern border with Turkey, which briefly spun out of government control after the reported mutiny of soldiers sent to suppress the dissent.

Those were not the first reports of defections, and none has yet added up to a serious threat. But in one sign of the government’s nervousness about the security forces’ loyalty, it has relied almost exclusively on the elite forces commanded by Assad’s brother Maher to implement the crackdowns.

And after three months of racing around the country putting down revolts, the unit is stretched, according to Amr Al Azm, a professor of Middle East history at Shawnee State University in Ohio who is also active in the Syrian opposition.

“It’s spreading itself very thin,” Azm said. “All areas are rising up, and the question is whether can they keep these troops out in the field on military operations ad infinitum.”

Staff writer Karen DeYoung in Washington contributed to this report.