Russian and Syrian jets escalated strikes on rebel-held Idlib and Hama provinces, several days after jihadi rebels opened an offensive against government-held parts of northwestern Syria, rebels and witnesses said on Sunday.

The bombing campaign in heavily populated civilian areas shattered six months of relative calm. Russian-inspired cease-fires had given a temporary reprieve to tens of thousands of people living in rebel-held northwestern Syria.

But now thousands of civilians who had been returning to their homes have headed back to the relative safety of refugee camps along the Turkish border, which are protected under Russian-Turkish understandings, residents said.