The Syrian Observatory for Human Rights said it confirmed the deaths "including four children who are siblings, two men and an unidentified person... as a result of Russian air strikes," in the Jisr al-Shughur countryside.

The children are all under 10 years old, said Rami Abdel Rahman, who heads the British-based Observatory.

Six of the victims are confirmed to be civilians, the Observatory said, adding that more people including women and children were still trapped under the rubble.

The victims are mostly displaced Syrians from neighbouring Hama province, said the monitor, which relies on a wide network of sources inside Syria.

Russia is a main 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 the 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.