"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.

Several other fighters were wounded in the strikes, with some in critical condition, said the Britain-based monitor, which relies on a wide network of sources inside Syria.

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.

HTS also controls parts of the adjacent Latakia, Hama and Aleppo provinces.

An AFP correspondent at the site said the jihadist group cordoned off the area after the strikes, which came shortly after midnight.

Russia has repeatedly struck the Idlib stronghold over the years.

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.

Moscow is a major ally of Damascus, and its intervention in Syria since 2015 helped to turn the tide in the regime's favour.

On August 5, three family members, all civilians, were killed when Russian warplanes struck the outskirts of Idlib city, the Observatory said at the time.

On June 25, Russian air strikes killed at least 13 people including nine civilians in Idlib province, in what the Observatory said was the deadliest such attack on the country this year.

A member of the Turkistan Islamic Party, a Uyghur-dominated jihadist group, was among the four fighters killed in those strikes, which also wounded at least 30 civilians, the monitor had said.

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

Syria's war has killed more than half a million people and forced around half of the country's pre-war population from their homes.

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

Since 2020, a ceasefire deal brokered by Damascus ally Moscow and rebel-backer Ankara has largely held in Syria's northwest, despite periodic clashes.