Syrian government warplanes and artillery pounded restive suburbs of Damascus on Friday, and anti-regime activists said a car bomb targeted an intelligence building north of the capital.
Fighting in Syria's civil war has flared in areas around Damascus as rebels seeking to topple President Bashar Assad try to push into the city. The rebel advances in the suburbs threaten the government's grip on its seat of power, prompting a punishing response from the military on rebel areas skirting the capital.
Anti-regime activists circulated a video they said showed an explosion near a military intelligence office in the town of Nabk, north of the capital. They had no information on casualties, and the government did not comment.
The blast came one day after a car bomb hit a gas station in the capital, killing 11 people, activists said. While no one has claimed responsibility for the attacks, they could be guerrilla strikes by rebel groups that lack the force to battle Assad's troops in the capital.
Syria's 21-month conflict has turned into a bloody stalemate that the United Nations says has killed more than 60,000 people, and it warns the civil war could kill many more this year.
On Friday, the Britain-based Syrian Observatory for Human Rights said government warplanes bombed suburbs of the capital, including Douma, where twin airstrikes killed more than a dozen people a day earlier.
The observatory also reported the explosion near the military intelligence building in Nabk. Fighting also raged south of the capital, where rebels have been trying to push into the city for weeks.
In neighboring Turkey, the first of 400 U.S. troops arrived to operate Patriot missile batteries intended to keep the violence from spilling over into the territory of the NATO country.
The ring of contested Damascus suburbs, known as the ghouta, is home to wealthy Syrian landowners and many Sunnis who flocked to the city from the countryside over the last decade.
"The environs of Damascus are very important for control of the city," said Andrew Tabler, a Syrian expert at the Washington Institute for Near East Policy. "Many are Sunni areas, intermixed with Alawite communities that ring Damascus. It's natural that the conflict would be in these areas."
Syria's insurgents are mainly members of the majority Sunni community; Assad is a member of the Alawite minority.
The rebels have used areas like the western suburb of Moadamiyat, which came under attack Friday, to try to choke off government access to the main military airport in Damascus. "The rebels want to liberate territory and deny the government logistical support," Tabler said.
The Americans who arrived at Incirlik air base in Turkey will operate two Patriot batteries being provided by the United States. Germany and the Netherlands are providing another four.
The batteries were deployed after Turkish towns were hit several times by cross-border shelling.
Turkey has been sharply critical of Assad, and many of the rebels fighting to oust the Syrian president use Turkey to organize and resupply themselves.