Rebels took control of an air defense brigade in Homs, the Syrian Observatory for Human Rights reported Sunday.
Syrian President Bashar Assad's forces later bombarded the nearby village of al-Ghento. Most of the brigade defected and retreated with the rebels before the bombardment began, the British-based watchdog reported.
Assad's forces killed at least 35 people in the attack on the Homs province, which was one of the biggest bombardments since a failed UN-mandated ceasefire in April, opposition activists said.
They said the Syrian army used artillery, mortars and rockets to hit opposition strongholds in the city of Homs and the towns of Qusair, Talbiseh and Rastan in central Syria.
Free Syrian Army rebels had been intensifying attacks in the area, the Syrian Network for Human Rights and other opposition campaigners said.
Assad's forces also carried out raids on neighborhoods in and around Damascus to try and flush out rebels who have been stepping up operations near security compounds in the capital.
United Nations efforts to bring peace to Syria - where a 15-month-old uprising against Assad has turned increasingly violent - have largely come to nothing, with both sides blaming the other for breaking the ceasefire.
Soldiers and militias loyal to Assad have killed at least 10,000 people, according to UN figures. The Assad government puts its own losses at more than 2,600 dead. Assad has blamed unspecified foreign-backed terrorists for the violence.
Among reports on the weekend violence, activist Abu Qassem said at least 500 rockets and shells had fallen on Rastan, 25 km north of Homs, since Saturday, and army helicopters were firing machine-guns into the area.
"The Free Syrian Army is far outgunned, but it is responding by mounting guerrilla attacks while trying to avoid direct exchange of fire," he said.
Rastan was once a reservoir of Sunni Muslim recruits for the military, whose senior ranks are dominated by members of Assad's minority Alawite sect, an offshoot of Shia Islam.
After Syria's revolt broke out in March last year and pro-democracy demonstrators in Rastan were killed, Sunni officers from the town began defecting.
Talbiseh to the south came under shelling and heavy mortar fire from loyalist troops after some soldiers from surrounding roadblocks defected on Saturday and drove two armored personnel carriers into the town, according to opposition sources there.
"Five people have been killed, including a woman and her one-year-old daughter. They were among the few civilians who had not fled Talbiseh," activist Abu Mohammad said by satellite phone.
Army shelling was also reported on Homs, concentrating on the neighborhood of al Khalidiya, inhabited mostly by Sunni tribal families from the desert, activists said.