Activists and state media reported heavy clashes and shelling in suburbs of the Syrian capital of Damascus and other parts of the country on Tuesday.
The Britain-based Syrian Observatory for Human Rights said some of the heaviest fighting is taking place in the Damascus suburb of Daraya.
The fighting showed opposition strength in the area of capital as the 22-month civil war drags on.
The Observatory and activist Mohammed Saeed, who is based near Damascus, said Syrian warplanes took part in bombing Daraya on Tuesday.
State-run news agency SANA said troops killed "tens of terrorists" in Daraya and nearby areas. The regime refers to opposition forces as "terrorists."
Daraya is few kilometres from the strategic military air base of Mazzeh, a western neighbourhood of the capital.