At least four of those killed in the strikes that hit a stone quarry and a nearby home west of Idlib city were civilians, said the Syrian Observatory for Human Rights, a Britain-based monitor that relies on an extensive network of sources on the ground.

The observatory said it was seeking to identify the other three casualties.

An AFP correspondent in the area saw ambulances ferrying victims from the site of the strikes, as large plumes of smoke rose overhead.

The house near the stone quarry was left completely destroyed, the correspondent said.

Russia, which did not comment immediately on the raid, is a key backer of President Bashar al-Assad's regime.

With Russian and Iranian support, Damascus clawed back much of the ground lost in the early stages of Syria's conflict, which erupted in 2011 when the government brutally repressed pro-democracy protests.

The last pocket of armed opposition to the regime includes large swathes of Idlib province and parts of the neighbouring Aleppo, Hama and Latakia provinces.

Hayat Tahrir al-Sham, headed by ex-members of Syria's former Al-Qaeda franchise, is the dominant group in the area but other rebel groups are also active, with varying degrees of Turkish backing.

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