Syrian state media reported later that an explosion was heard in a military area in Dummar, a northwestern suburb of the capital Damascus. Syrian state TV said the blast was the result of an explosion in an arms depot that triggered some fires in nearby brush.
State TV gave no further details about the cause of the blast or whether there were fatalities. In northwest Syria, fighting intensified as government forces pressed their offensive toward Idlib province, the last major rebel stronghold in the country's lengthy civil war.
The Britain-based Syrian Observatory for Human Rights and the opposition's Syrian Civil Defense said at least 10 civilians were killed in Saturday's airstrikes and shelling of rebel-held villages and towns.
Syrian state media said militants shelled government-held areas causing material damage. The Observatory said Saturday's fighting alone left 26 troops and pro-government gunmen dead along with eight militants.
The Ibaa news agency, the media arm of al-Qaida-linked Hayat Tahrir al-Sham, or HTS, said the militants killed and wounded "a whole group" of Syrian soldiers in their second failed attempt to advance toward a strategic hill.
Six weeks of violence has driven nearly 300,000 people from their homes. Many are living under olive trees, in tents or unfinished buildings, crammed into overcrowded shared rooms. More than 300 civilians have been killed since fighting broke out on April 30.