"Russian warplanes carried out air strikes on the western outskirts of Idlib city, targeting a military base belonging to Hayat Tahrir al-Sham (HTS)... killing at least eight fighters," said Rami Abdel Rahman, who heads the Syrian Observatory for Human Rights.

Jihadist group HTS, led by Syria's former Al-Qaeda affiliate, controls swathes of Idlib province, parts of which form the last bastions of armed opposition to President Bashar al-Assad's rule.

An AFP correspondent at the site said the strikes, which came shortly after midnight, targeted an area on the outskirts of Idlib city near swimming pools.

Syria's civil war broke out in 2011 after the government's repression of peaceful demonstrations escalated into a deadly conflict that pulled in foreign powers and global jihadists.

With Russian and Iranian support, Damascus has clawed back much of the territory it had lost to rebels early in the conflict.

The war has killed more than half a million people and displaced millions.

The rebel-held Idlib region is home to about three million people, around half of them displaced from other parts of the country.