Another 45 civilians were wounded in the strikes across the jihadist-held Idlib region, according to the Syrian Observatory for Human Rights.

Those killed included three people in Idlib city, which until Friday had been spared strikes by the regime and its Russian ally since they stepped up bombardment of the region more than two months ago.

"It's the first time that the raids hit the centre of Idlib, after being confined until now to its suburbs," said Observatory head Rami Abdel Rahman.

Last month, a civilian was killed in an air strike on the outskirts of the regional capital, considered the stronghold of Syria's former Al-Qaeda affiliate Hayat Tahrir al-Sham (HTS).

The group in January took full administrative control of the Idlib region, home to three million people, although other jihadist groups and rebel factions are also present.

Russian and regime aircraft have ramped up strikes on Idlib since the end of April, killing more than 580 civilians.

Rebel and jihadist fire has killed 45 civilians over the same period, the Britain-based Observatory says.

Friday's air strikes hit residential buildings in one of the city's largest squares, Sabaa Bahrat, an AFP photographer said.

Ambulances were dispatched to the scene to tend to the victims, he added.

Meanwhile in neighbouring Hama province, six children were wounded by opposition fire in the regime-held area of Karnaz.

Fierce clashes have raged in the northern sliver of Hama province in recent days, killing more than 120 since late Wednesday, according to the Observatory.

The recent uptick in violence has forced 330,000 people to flee their homes, according to the United Nations.

The Idlib region is supposed to be protected from a massive regime offensive by a September deal between Russia and rebel backer Turkey, but a buffer zone planned under that accord was never fully implemented.

Syria's war has killed more than 370,000 people and displaced millions since it started in 2011 with a brutal crackdown on anti-government protests.