IS recaptures 'last stronghold' in Syria from regime, Hizballah

Islamic State group fighters have retaken the town of Albukamal in eastern Syria from regime loyalist troops and allied Iranian-backed militias, a week after Damascus claimed to have captured the city.

According tribal leaders, residents and a war monitor who spoke to Reuters on Monday, fighters from Lebanese Shia group Hizballah in Syria joined forces with Iraqi Shia fighters who crossed the border to take Albukamal by surprise.

The militants had been hiding inside tunnels in the heart of the city they said they had taken on Wednesday.

The Shia fighters had launched a ground offensive on the city, in Syria's eastern Deir az-Zour province, after months of mainly Russian heavy bombardment, which has left dozens of civilians dead and caused widespread destruction.

"Islamic State group militants began surprise attacks with suicide bombers and rocket attacks after the Iranian militias were duped that Daesh had left the city," Qahtan Ghanam al-Ali, a tribal leader, told Reuters.

The Syrian army had on Thursday declared victory over IS, claiming it had killed many militants while scores surrendered. It said the capture of Albukamal marked the collapse of the militants' three-year reign in the region.

The army made no mention of the loss of Albukamal, but Hizballah media said intensive air strikes hit IS hideouts in the western countryside of the city.

The offensive was spearheaded by elite forces from Hizballah fighting inside Syria alongside an array of Iraqi and Afghan Shia militias that had entered from Iraq, a commander in that alliance told Reuters.

"These militant attacks lead to big human losses in the ranks of fighters supporting the regime," the UK-based Syrian Observatory for Human Rights said.

Albukamal, a major supply and communications hub for the ultra-hardline militants between Syria and Iraq, was a big prize for the Iranian-backed militias.

The militants' control of the city and its sister border town of al-Qaim on the Iraqi side had disrupted the strategic Baghdad-Damascus highway that had long been a major arms supply conduit by Iran to its Syrian ally.

On Sunday, jets believed to be Russian intensified their third day of bombing of Albukamal and its outskirts, with at least 50 civilians - mostly women and children - killed since Friday, the monitor and residents said.

In retaliation for their losses, Iranian militias who were forced to withdraw shelled villages east of the city where hundreds of families who fled Albukamal had found temporary refuge, the UK-based war monitor said.

In one air strike on the town of Sukariya, east of the city, at least 30 people were killed, mostly women and children from three families, two former residents of the city said.

Other air strikes hit villages of Marshada and Sousa near the river crossing where hundreds of civilians were targeted as they fled in boats and dinghies, they added.

Albukamal has been a target of intensive strikes believed to be conducted by Russia across Deir az-Zour province which has killed hundreds of civilians in recent months, according to the monitor and local figures.

Military experts and Syrian opposition figures said Russia has stepped up a "scorched earth" policy in the province with its aerial bombing in recent months to secure a rapid victory at any price for its military and its allies.