Surman (Syria) (AFP) - Two days of clashes between regime forces and armed groups in Syria's last major opposition bastion have killed nearly 70 on both sides, a war monitoring group said Sunday.

The battles in the northwestern province of Idlib are the most violent there since a Russian-brokered ceasefire agreement went into effect in late August, said the head of the Syrian Observatory for Human Rights.

On Sunday morning, clouds of smoke rose over the Maaret al-Numan region as warplanes pounded jihadists and allied rebels in positions they had recently recaptured from regime forces, said an AFP correspondent.

Residents of affected villages fled north to escape the fighting, adding to the tens of thousands who have already flooded out of the province's violence-plagued south since an escalation started earlier this year.

The Observatory on Sunday put the death toll from fighting at 69 combatants since battles started the previous day.

At least 36 regime forces were among those killed.

It said an attack led by Syria's former Al-Qaeda affiliate on several regime positions had initially sparked the fighting.

Overnight, the Syrian army backed by Russian warplanes launched a counter-push to reclaim territory it had lost in the battles, according to the Britain-based war monitor.

Regime forces have since regained lost ground but violent clashes are ongoing, the war monitor and an AFP correspondent said.

The Idlib region, home to around three million people including many displaced by Syria's eight-year civil war, is controlled by the country's former Al-Qaeda affiliate.

The Hayat Tahrir al-Sham jihadist alliance also controls parts of neighbouring Aleppo and Latakia provinces where battles with regime forces have also recently taken place.

The region is one of the last holdouts of opposition to forces of Syrian President Bashar al-Assad.

A ceasefire announced by Russia in late August has reduced violence in the area.

Between the end of April and the end of August, Idlib was pounded ceaselessly by Syrian soldiers backed by Russian air power.

The Observatory estimates that nearly 1,000 civilians were killed in that period, and the UN says that more than 400,000 people were displaced.

The war in Syria has killed more than 370,000 people and displaced millions since it erupted in 2011.