Air strikes on a market in Syria's Al-Qaeda-held city of Idlib killed at least 21 civilians Sunday, as hundreds fled a besieged ISIS bastion near the Turkish border, AFP reports.

Five children were among those killed in the air raids on Idlib, which is held by Al-Qaeda affiliate Al-Nusra Front and its allies, the Syrian Observatory for Human Rights said.

It was not clear who carried out the Idlib strikes, but the Observatory has reported previous air raids by the regime and its Russian ally on Idlib province, which is also controlled by Al-Nusra and rebel allies.

In Maaret al-Numan, an area south of the provincial capital, unidentified warplanes also killed at least six civilians including a woman and her four children, the Observatory said.

Russia launched air strikes in support of the Damascus regime in September, allowing forces loyal to President Bashar al-Assad to advance against the rebels and ISIS.