(CNN) -- Armed plainclothesmen broke up anti-government demonstrations with gunfire after weekly prayers in the Syrian city of Hama on Friday, opposition activists said, while government troops extended their clampdown to another town nearby.
Three opposition groups -- the Local Coordination Committees of Syria, Avaaz and the London-based Syrian Observatory for Human Rights -- each reported that 15 people were killed Friday in Syria.
Because the government has restricted international journalists from reporting in Syria, CNN was not able to independently confirm the death tallies.
Government troops moved into the town of Khan Sheikhoun, north of Hama, opposition activists and human rights groups said. Syria's state-run SANA news agency reported that the troops were fighting armed gangs in the embattled northwest province of Idlib, an acknowledgment by President Bashar al-Assad's government of military operations that human rights groups allege have resulted in the killings of civilians.
At least one woman was killed in clashes between demonstrators and Syrian forces, who rolled into Khan Sheikhoun at dawn with tanks and armored personnel carriers, according to the Observatory for Human Rights, which cited reports from opposition activists in the city.
The identities of the opposition activists were withheld by the rights group at their request out of concerns for their safety.
And in Hama, where military units withdrew earlier this week, busloads of plainclothes security forces opened fire to break up anti-government protests after Friday prayers at local mosques, an opposition activist there told CNN. There were reports of casualties, but their number and severity were unknown, he said.
The activist said several volleys of gunfire were used to disperse worshippers at a mosque he attended. He and another witness said similar incidents had occurred at several other mosques.
The second witness said that, as soon as the imam at his mosque finished prayers, he heard gunshots and thugs cursing and making threats.
"They were making sure no one demonstrates," he said. As people left the mosque, "the security forces started detaining left and right."
He said a cousin told him one person was killed.
Activists took to the streets again in Homs, despite the killing on Wednesday and Thursday of more than two dozen residents there, activists said. Videos showed the determination and defiance of the demonstrators. One video showed demonstrators being shot at by security forces, then regrouping and returning to the streets.
In Syria's second-largest city, Aleppo, video posted on YouTube showed what appeared to be protesters carrying a wounded comrade to safety.
Outside Damascus, in Harasta, another video showed demonstrators fleeing gunfire.
Al-Assad is under increasing pressure from the West and from fellow Arab states to halt the clampdown. The United States has has stopped short of explicit calls for him to step down, but Secretary of State Hillary Clinton said Friday that al-Assad "has lost the legitimacy to lead, and it is clear that Syria would be better off without him."
"We urge those countries still buying Syrian oil and gas, those countries still sending Assad weapons, those countries whose political and economic support give him comfort in his brutality, to get on the right side of history," Clinton told reporters in Washington.
Oil and gas make up about a quarter of the Syria's economy, according to the International Monetary Fund. In addition, Clinton said the United States and its allies are trying to help opposition groups "create a unified vision of what an inclusive participatory democratic system in Syria could look like."
The conflict in Syria erupted five months ago when Syrian forces suppressed protests in the southern city of Daraa. Anti-government fervor caught on nationwide as more protests were met with tougher crackdowns. By Wednesday, the death toll had reached 2,417, including more than 2,000 civilians, said the Local Coordination Committees of Syria. The Syrian Observatory for Human Rights put the toll at 2,182.
Friday's fighting in Khan Sheikhoun was reported just hours after SANA, the news agency, said security had been restored in Hama. But the Syrian Observatory said armored personnel carriers and machine guns mounted on vehicles remained in the Hama late Thursday, and 27 people have been detained.
In June, thousands of residents of another town in Idlib province fled their homes for Turkey after Syrian troops moved in. The latest operations in the province have renewed fears that others may again cross the border to escape the five-month-old crisis.
One person was killed during a military raid in Saqba, on the outskirts of Damascus, the Syrian Observatory said, citing reports from opposition activists in the city.
In northern Syria, about 200 people were arrested Thursday in Saraqib after troops seized the city, according to the Syrian Observatory group, which cited reports from opposition activists in the city.
CNN's Amir Ahmed, Arwa Damon, Nada Husseini and Yesim Comert contributed to this report.