Clashes on the edge of an opposition and rebel bastion in north-western Syria have killed at least 42 fighters on both sides in 24 hours, a monitor said on Monday, after regime bombardment on the region devastated health services.
The demilitarised region has come under increasing fire by the regime and its ally Russia in recent weeks, despite the months-old buffer zone deal designed to shield it from any regime offensive.
Turkish Defence Minister Hulusi Akar and his Russian counterpart Sergey Shoigu discussed by phone developments in Idlib province, Turkey's defence ministry said on Tuesday.
Measures to reduce tension in the region were also discussed, according to the ministry.
Assad's fight for last major holdout
Hayat Tahrir al Sham (HTS), a former Al Qaeda affiliate in Syria, controls most of Idlib province as well as parts of neighbouring Aleppo, Hama and Latakia provinces.
Syrian regime troops on Monday captured five small villages and a hill in Idlib province, pro-Assad media said.
The Syrian Observatory for Human Rights said 16 regime loyalists and 19 opposition fighters and rebels died from Sunday to Monday in clashes in the area of Jabal al Akrad in Latakia province, which lies on the opposition and rebel bastion's northwestern edge.
Russian and regime aircraft bombarded the area on Monday, said the Britain-based war monitor.
Russian air strikes hit a branch of the White Helmets rescue volunteers in the town of Kafranbel on the southern end of the stronghold, rendering it unable to operate, the Observatory and a rescue worker said.
At the White Helmets facility, an AFP correspondent saw a concrete roof had collapsed in on a bulldozer and other vehicles, and the ground was covered with rubble.
"Two high-explosive missiles hit the centre" just minutes after its personnel had headed out to the site of strikes in a nearby village, Oneida Zikra, the civil defence chief for the area, said.
To the south, rocket fire killed one child in the regime-held town of Suqaylabiyah in Hama province, the Observatory and the regime news agency SANA said.
HTS and its allies launched a counter-attack late Monday, bombing areas in the north of the province and sparking fierce clashes on the ground, according to the Observatory.
Idlib's three million inhabitants are supposed to be protected by a September buffer zone deal signed by Russia and Turkey.
But an uptick in air strikes and shelling displaced 180,000 people between April 29 and May 9 alone, the United Nations says.
The Observatory says 119 civilians have been killed in the bombardment since late April.
On Monday, the UN Office for the Coordination of Humanitarian Affairs said 18 health facilities had been knocked out of service in a little over a fortnight, two of them hit twice.
"Attacks on health facilities in north-west Syria continue to exact a devastating toll on the civilian population," said OCHA spokesman for Syria David Swanson.
"Such violence is appalling. Hospitals are and must remain a place of sanctuary and unequivocal neutrality," he said.
UN-linked aid groups on Saturday said they had suspended activities in parts of the region, as the violence has jeopardised the safety of humanitarian workers.
In a filmed interview released on Sunday night, HTS chief Abu Mohammad al Jolani urged supporters to "take up weapons" to defend Idlib.
The spike in violence signalled "the death of all previous agreements and conferences," he said.
In a joint statement on Monday, Britain, France and Germany said the military escalation in northwestern Syria "must stop."
"The current brutal offensive by the Syrian regime and its backers on millions of civilians living in the area is not about fighting terrorism. It is about pushing forward the ruthless reconquest by the regime," they said.
Damascus has not announced a wide offensive, but analysts believe there could be a limited military operation.
The civil war in Syria has killed more than 370,000 people and displaced millions since it started with the brutal repression of anti-regime protests in 2011.