Syrian warplanes are pounding opposition strongholds around Damascus and in the north, activists said, as President Bashar Assad's regime intensifies air strikes against rebels seeking to topple him.

The Britain-based Syrian Observatory for Human Rights, which gathers reports from a network of activists, said government jets carried out five strikes on Wednesday morning in the eastern Ghouta district, a rebel stronghold close to the capital.

Three air strikes also hit the rebel-held city of Maaret al-Numan, which straddles a key supply route from Damascus to Aleppo in the north.

No casualties were reported in the latest strikes, the Observatory said.

However, at least 185 people were killed on Tuesday, pushing the total death toll from the relentless fighting in Syria to more than 36,000, said Rami Abdul-Rahman, the group's president.