BEIRUT — Clashes between Syrian regime forces and armed groups in the country's last major opposition bastion have killed more than 80 on both sides in the past 24 hours, despite UN calls for de-escalation, a war monitor said on Friday.

The Britain-based Syrian Observatory for Human Rights said 42 militants and nine rebels had been killed in battles with regime forces in the northwestern province of Idlib since Thursday night.

The fighting near the militant-held town of Maaret Al-Numan also killed 30 Syrian regime loyalists, the Observatory said.

Warplanes from regime ally Russia pounded areas around Maaret Al-Numan and the nearby town of Saraqeb with a series of air strikes, said the Observatory which relies on a network of sources across Syria.

The flare-up triggered a wave of displacement from nearby areas, said a correspondent in Maaret Al-Numan.

Yasser Ibrahim Al-Dandal said he was fleeing with his family to olive groves in northern Idlib, where they would sleep out in the open.

"Hundreds of rockets hit Maarat Al-Numan," he said. "The situation is very bad."

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

Pro-government forces launched a blistering offensive against the region in April, killing around 1,000 civilians and displacing more than 400,000 people from their homes.

Since August, the area has supposedly been protected by a ceasefire announced by Moscow, but the regime of President Bashar Assad has repeatedly vowed to retake the area and the Observatory says deadly bombardment and skirmishes have persisted.

The United Nations this week condemned a deadly rise in violence after the Observatory reported that regime air strikes and artillery fire had killed 23 civilians on Tuesday.

Najat Rochdi, senior humanitarian adviser to the UN's Syria envoy, called for "immediate de-escalation".

Syria's war has killed over 370,000 people and displaced millions from their homes since it began in 2011 with the brutal repression of anti-government protests. — AFP