BEIRUT (Reuters) - An air raid on a rebel-held area of northwestern Syria killed 20 people including 16 children fleeing an earlier strike on a school, rescue workers said on Wednesday.

The Syrian Civil Defence rescue service, which operates in opposition areas, said the air raid took place in the village of Kafr Batikh in the eastern part of Idlib province on Wednesday.

A war monitor, the Britain-based Syrian Observatory for Human Rights, gave the same number of dead and said that 15 were from one family.

Idlib is the largest, most populous area still held by rebels seeking to oust Syrian President Bashar al-Assad, whose forces are backed in the war by Russian air power.

Assad and his allies are also attacking rebels in eastern Ghouta, near Damascus, in an offensive that has involved intense bombardment. On Wednesday, rebel sources in one part of eastern Ghouta said there was a deal with the government for insurgents there to leave the area for Idlib under safe passage.

On Monday an airstrike in Arbin in eastern Ghouta killed 15 children and two women sheltering in the basement of a school, the Observatory said.

The government and Russia describe the rebel groups in Syria as terrorists. They have accused the Western-funded Civil Defence, sometimes also called the White Helmets, of working with terrorist groups and fabricating evidence of civilian casualties, which it denies.