At least seven people were killed and dozens wounded after Syrian rebels attacked in the central Syrian town of Hama, a traditional symbol of dissent against four decades of Assad family rule.
Most of the casualties were civilians.
Activists said it was the first time in six months that a major clash had reached Hama.
"The operation is an attempt to alleviate some pressure on fighters in the countryside of Hama as well as in nearby provinces," an activist who called himself Safi al-Hamawi told Reuters via Skype.
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But he questioned the utility of the effort, raising concerns it may not be extensive enough to help.
Video uploaded by activists showed heavy machinegun and rocket fire amid cries of "God is great" from rebel fighters in Hama.
One video showed rebels raising a black Islamist flag over a charred and bullet-scarred school they stormed on Thursday.
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They said it had been used as a military base and detention center by soldiers and pro-Assad militias.
"This was one of the worst regime sites in the city. The soldiers treated residents harshly and in a sectarian manner," said an activist using the name Abu Adnan, speaking from Hama.
Hama has long been associated with opposition to the Assad family. Assad's father, who ruled Syria for 30 years until his death in 2000, crushed an armed Islamist revolt in Hama in 1982, killing many thousands of people and razing parts of the city.
Reuters contributed to this report.