A regime air strike targeted the Baba Amr area of Homs city on Wednesday, four days after rebels infiltrated the district which has seen some of the fiercest battles in Syria's two-year-old revolt, a watchdog said.
The Syrian Observatory for Human Rights also said two children were killed by mortar fire in Damascus.
Other clashes raged near the sensitive border with Lebanon, it said, while the regime's intelligence forces used heavy machine-gun fire to target rebel enclaves around the ancient city of Palmyra.
"A warplane carried out a new raid targeting the district of Baba Amr," said the Britain-based Observatory, which relies on a network of activists, doctors and lawyers for its information.
Rebel forces have re-entered Baba Amr a year after the district fell back into army control.
Clashes have also raged in parts of the southwestern district of Homs, while rebels in the heart of Syria's third city are reportedly holding out against an escalated army offensive aimed at crushing the insurgency there.
Rebels and troops have both sustained heavy losses over the past week in the city of central Syria, according to the Observatory.
And on the border with Lebanon, "four rebel fighters were killed in clashes against troops in the village of Jousiyeh."
In the capital, at least five people, among them two children, were killed and 30 wounded when mortar rounds crashed into Fahameh district near the conflict-torn area of Kfar Sousa, said the Observatory.
"The number of casualties is likely to rise," it said, adding that the mortar rounds landed near an orphanage and a state security building.
"Rebels fire almost daily onto areas in central Damascus. Because of the nature of their weapons, their shots are inaccurate," Observatory director Rami Abdel Rahman told AFP.
In the northwest, clashes raged at Hish in Idlib province as regime forces "fought to break the (rebel) siege on the Wadi Deif base" nearby, said the Observatory.
The insurgents laid siege to Wadi Deif last October.
In the northern city of Aleppo, warplanes carried out several strikes near Minnigh air base, the scene of fierce fighting since rebels launched an all-out campaign to seize airports in the province on February 12.
Wednesday's violence came a day after at least 110 people were killed across the country, the Observatory said.
The United Nations says that Syria's conflict has left at least 70,000 people dead since mid-March 2011.