Syrian regime and extremist-led rebel forces clashed on Thursday on the edge of an opposition bastion in north-west Syria after a rebel advance that killed 56 fighters overnight, a war monitor said.
Russian and regime aircraft have stepped up their deadly bombardment of Idlib region – administered by Syria's former Al Qaeda affiliate Hayat Tahrir Al Sham and home to about three million people – since late April, despite a months-old international truce.
Clashes have also raged on the edges of the region, including in the north of Hama province.
Late on Wednesday, HTS and allied rebels took control of Hamameyat village and hilltop, in clashes that killed 32 regime fighters and 24 fighters within the insurgent ranks, the Syrian Observatory for Human Rights said.
"The fighting is ongoing as regime planes and artillery pound the area," the head of the Britain-based monitor Rami Abdurrahman said on Thursday morning.
HTS spokesman Abu Khaled Al Shami said its fighters and rebels attacked after dark, taking control of the "heavily fortified" hill from fighters loyal to President Bashar Al Assad.
Naji Mustafa, a spokesman for the allied National Liberation Front rebel grouping, said: "The hill is very strategic because it overlooks ... supply routes to enemy forces."
A September deal between Russia and rebel backer Turkey was supposed to avert a massive regime offensive on Idlib, but it was never fully implemented and HTS took full administrative control in January.
More than 550 civilians have been killed in regime and Russian air strikes on north-west Syria since the end of April, according to the Observatory.
Air strikes on Wednesday alone killed at least 15 civilians, among them four children, including in raids that knocked a hospital out of service, the monitor said.
The United Nations says 25 health facilities in the region have been hit, while the fighting has forced 330,000 people to flee their homes.
Syria's war has killed more than 400,000 people and displaced millions since it started in 2011 with a brutal crackdown on anti-government protests.
International diplomatic efforts have so far failed to end the fighting, with the Syrian regime rejecting the opposition demand for Mr Al Assad to step down. However, the UN envoy for Syria raised hopes of an agreement on setting up a constitutional committee, a long-awaited step in the stalled peace process, after talks in Damascus on Wednesday.
"I believe we have made a very solid progress and we are very close to have agreement on establishing the constitutional committee," Geir Pedersen told reporters after meeting Syrian Foreign Minister Walid Al Muallem.
The United Nations wants to convene the committee as a next step in efforts to find a political solution to end the war in Syria, but there has been no agreement so far on who should be on it.
A Syrian foreign ministry statement said significant progress had been made in the talks, but also reiterated its previous stance that the constitutional committee should be a purely Syrian affair.
Mr Pedersen also called for a return to stability in Idlib province and said the truce there agreed last year between Russia and Turkey should come back into force.
Russia is along with Iran the main supporter of President Al Assad, who now controls most of the country, while Turkey backs some of the rebel groups in Idlib and adjacent areas.
