Syrian regime forces retook control of the last southern holdout of the Islamic State group Saturday, as a monitor said air strikes killed dozens in a remaining jihadist pocket in the country's east.
More than seven years into Syria's grinding civil war, multiple forces are battling to push IS out of its remaining scraps of territory in the country.
On Saturday, regime forces retook the southern area of Tulul al-Safa as the jihadists pulled back into the desert after months of fighting, the Britain-based Syrian Observatory for Human Rights said.
Pro-government fighters regained control of the volcanic plateau between the provinces of Damascus and Sweida "after IS fighters withdrew from it and headed east into the Badia desert", Observatory chief Rami Abdel Rahman said.
The withdrawal likely came "under a deal with the regime forces" after weeks of encirclement and air raids, he said.
In recent weeks, air strikes on the Tulul al-Safa pocket had increased and hundreds of regime fighters were sent as reinforcements, the Observatory said.
State news agency SANA reported regime forces had made "a great advance in Tulul al-Safa" and said they were combing the area for any remaining jihadists.
That victory has whittled down the jihadists group's territorial control to a single pocket in the east of the country, where it faces a separate assault by US-backed forces.
- Civilians killed in far east? -
A Kurdish-Arab alliance supported by a US-led coalition has been fighting to expel IS from that far eastern patch near the Iraqi border since September.
The Observatory said coalition air strikes early Saturday on the village of Abu al-Husn in Deir Ezzor province killed 43 people, including 36 family members of IS fighters.
"It's the highest death toll in coalition air strikes since the Syrian Democratic Forces (SDF) launched its attack against the IS pocket" in September, Abdel Rahman said.
Seventeen of those killed were children, he said, while seven of the dead remained unidentified.
A spokesman for the US-led coalition confirmed strikes in the area of Abu Husn, but said they had not harmed any non-combattants.
"No civilian casualties are associated with the strikes in question," spokesman Sean Ryan told AFP.
"The coalition takes great measures to identify and strike appropriate ISIS targets in order to avoid non-combatant casualties," he said, using another acronym for IS.
The Observatory says coalition air raids have killed 234 civilians including 82 children since September 10, when the SDF launched the offensive on the eastern IS holdout.
It says 625 jihadists have been killed in strikes and clashes in the area during the same period.
The SDF assault was slowed by a fierce jihadist fightback, and then briefly put on hold to protest Turkish shelling of Kurdish militia positions in northern Syria.
- 'Careful advance' -
SDF commander Redur Khalil said Saturday that operations were ongoing.
"There has been an advance on the ground in the past days but it is a careful advance due to fields of landmines, trenches, tunnels and barricades set up by IS," he told AFP.
IS overran large swathes of Syria and neighbouring Iraq in 2014, proclaiming a "caliphate" in land it controlled.
But the jihadist group has since lost most of it to various offensives in both countries.
Regime forces had been fighting IS in Tulul al-Safa since a deadly jihadist attack in July.
That fighting has killed 240 regime fighters and 420 IS jihadists, the Observatory says.
In the July 25 attack, IS killed more than 260 people, most of them civilians, in a wave of suicide bombings, shootings, and stabbings across Sweida province in the bloodiest assault on the Druze minority of the war.
Followers of a secretive offshoot of Islam, the Druze are considered heretics by the Sunni extremists of IS.
Syria's war has killed more than 360,000 people since it erupted in 2011 with the brutal repression of anti-government protests.
Since 2014, the US-led coalition has acknowledged direct responsibility for over 1,100 civilian deaths in Syria and Iraq, but rights groups put the number killed much higher.