BEIRUT — Clashes between Syrian government forces and jihadists have killed 43 fighters in the country's northwest, where the regime and its Russian ally have stepped up bombardment in the past few days, a monitor said.

Jihadists also fired rockets at a Russian air base in the region but were repelled, with the attack causing no casualties or damage, the Russian defence ministry said in a statement.

Twenty-two pro-government fighters were among those killed in fierce fighting in the northern countryside of Hama province, the Britain-based Syrian Observatory for Human Rights said on Monday.

Twenty-one jihadists, including members of Al-Qaeda's former Syrian branch, Hayat Tahrir al-Sham (HTS), and its ally the Turkistan Islamic Party, were also killed, the war monitor said.

The fighting came as regime forces advanced on two villages and a strategic hilltop in the region, it said.

State news agency SANA said Syrian troops launched "intensive operations," targeting supply lines and areas where armed groups operate in northern Hama and neighbouring Idlib.

The region held by HTS has faced intensifying bombardment in the past month, prompting a new wave of displacement.

Earlier Monday, five civilians were killed in shelling and air strikes on Idlib and neighbouring areas by Syrian government forces and their Russian allies, said the Observatory.

An AFP photographer in Idlib saw several houses completely destroyed by recent attacks.

One man who lost his wife, his daughter-in-law, and his two grandchildren during shelling overnight prepared a pickup truck to relocate surviving members of his family.

"I don't know where I'm going," he said.

'Humanitarian disaster' 

United Nations Secretary-General Antonio Guterres urged the warring parties to protect civilians and respect a ceasefire.

Guterres "calls for an urgent de-escalation of the situation as the holy month of Ramadan begins and urges the parties to recommit fully to the ceasefire arrangements of the memorandum signed on 17 September 2018", a statement read.

More than 140,000 civilians have been forced to flee attacks since February, Refugees International said on Monday.

"It is difficult to overstate the urgency of this looming humanitarian disaster if nothing is done to protect these people," the non-governmental organisation said in a statement.

Escalated attacks have hit schools and medical facilities, according to the UN.

Since 28 April, at least seven healthcare facilities have reportedly been struck, including four in Hama and three in Idlib, said David Swanson of the UN Office for the Coordination of Humanitarian Affairs.

Russia and rebel-backer Turkey in September inked a buffer zone deal to prevent a massive regime offensive on the Idlib region, near the Turkish border.

But the region of some three million people has come under increasing bombardment since HTS took full control of it in January.

A statement by the Russian defence ministry said that the Hmeimim airbase in Latakia province neighbouring Idlib was the target Monday of rocket fire. — AFP