The army fired rockets at Daraya and Moadamiah, suburbs of the capital city, the Syrian Observatory for Human Rights said.
The group said it feared government troops were massing for a ground assault, Voice of America reported.
About 400 U.S. and Dutch NATO troops were massed on Turkey's Syrian border amid fears besieged President Bashar Assad was poised to use chemical weapons.
The soldiers were readying Patriot missiles three days after NATO agreed to deploy the MIM-104 Patriot surface-to-air missile system in Turkey. Ankara had requested the installations as a defense against a Syrian missile attack, possibly with chemical weapons.
"Nobody knows what such a regime is capable of and that is why we are acting protectively here," German Foreign Minister Guido Westerwelle said of NATO's move.
U.S. Defense Secretary Leon Panetta said Thursday the latest intelligence reports heightened fears Assad would use chemical weapons on the rebels trying to oust him.
"The intelligence that we have raises serious concerns that this is being considered," he said.
Over four decades, Syria has amassed one of the largest undeclared stockpiles of chemicals in the world, including huge supplies of mustard gas, sarin nerve agent and cyanide, the CIA says.
Syria denounced the NATO action and the U.S. and German statements.
Syrian Deputy Foreign Minister Faisal Miqdad told pro-Assad Lebanese satellite TV station al-Manar, affiliated with the Shiite militant group Hezbollah: "Syria stresses again, for the 10th, the 100th time, that if we had such [chemical] weapons, they would not be used against its people. We would not commit suicide."
Miqdad accused the United States and pro-opposition European countries of "conspiring" to create the impression the Assad regime would use chemical weapons to justify an intervention.
The high-stakes actions came as U.S. Secretary of State Hillary Clinton held a surprise meeting with Russian Foreign Minister Sergey Lavrov and U.N.-Arab League special envoy on Syria, Lakhdar Brahimi, to broker a deal that would lead to Assad's ouster and a transitional government's installation.
The U.S. State Department said the 40-minute meeting, which Brahimi called, was a "constructive discussion focused on how to support a political transition in practical terms."
Brahimi said afterward his goal was to "put together a peace process" that would build on a political transition strategy Washington and Moscow worked out in Geneva in June. That strategy quickly came undone over enforcement issues, officials said at the time.
"We haven't taken any sensational decisions," Brahimi said. He called Syria's situation "very, very, very bad."
Clinton told reporters before the meeting, "We have been trying hard to work with Russia to try to stop the bloodshed in Syria and start a political transition for a post-Assad Syrian future."
She added, "Events on the ground in Syria are accelerating, and we see that in many different ways."
The opposition Local Coordination Committees of Syria said at least 89 people were killed in Syria Thursday. It said Syrian troops shelled at least 248 points, with 13 points shelled by warplanes, mostly in the Damascus suburbs.
Two points were hit with cluster bombs and four with barrel bombs, the group said.
Cluster bombs are air-dropped or ground-launched and release or eject smaller sub-munitions, or explosive "bomblets." Barrel bombs are large oil drums packed with TNT, oil and chunks of steel and dropped from helicopters. These improvised weapons are intended to cause maximum death and destruction, British newspaper The Daily Telegraph reported.