The British-based Observatory, which monitors Syria through a network of sources inside the country, said six members of the security forces were killed in fighting with rebels in the town of Al-Ashaara in Deir al-Zor.
A further five people, including an army defector, were killed in army shelling of the town, it said.
In the centre of the country, where Free Syrian Army rebels have been intensifying attacks on forces loyal to President Bashar al-Assad, the army shelled Rastan and the city of Homs and conducted army offensives in Hama and Idlib provinces.
Video posted on the Internet by activists showed what they said were helicopters firing missiles at targets in Rastan.
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 U.N. figures. The Assad government puts its own losses at more than 2,600 dead. Assad has blamed unspecified foreign-backed terrorists for the violence.
The Observatory said four members of the security forces and a civilian were killed when a bomb exploded near a security patrol in the northern city of Idlib.