Syrian rebels advanced into an Islamic State-held town at the border with Iraq on Wednesday, a rebel commander told Reuters, in a new US-backed offensive aimed at cutting the jihadists' self-declared caliphate in two.
The operation aiming to capture the eastern Syrian town of Al-Bukamal, which began on Tuesday, adds to the pressure facing Islamic State as it faces a separate, US-backed offensive in northern Syria aimed at driving it away from the Turkish border.
The offensive is being waged by rebels of the "New Syria Army" formed some 18 months ago from insurgents driven from eastern Syria at the height of Islamic State's rapid expansion in 2014. Rebel sources say it has been trained with US support.
"The clashes are inside the [town] and matters are not yet settled," said the rebel commander of the Asala wa-al-Tanmiya Front, one of the main elements of the New Syria Army. The rebel forces entered the town at dawn, he said.
The Syrian Observatory for Human Rights said the offensive was being mounted with backing of Western special forces and US-led air strikes.
Islamic State's capture of Al-Bukamal in 2014 effectively erased the border between Syria and Iraq. Losing it would be a huge symbolic and strategic blow to the cross-border "caliphate" led by Abu Bakr al-Baghdadi.
The town is just a few kilometers from the Iraqi frontier in Deir al-Zor province, nearly all of which is under Islamic State control.
The US-led campaign against Islamic State has gone up a gear this month, with an alliance of militias including the Kurdish YPG launching a major offensive against IS in the city of Manbij in northern Syria. In Iraq, the government this week declared victory over Islamic State in Falluja.
Rebels hit by Russians
Syrian rebel sources say the rebel force has received military training in US-run camps in Jordan, but most of their training was now being conducted in a main base at al-Tanf, a Syrian town southwest of Al-Bukamal at the border with Iraq.
The New Syria Army's base in al-Tanf was hit twice earlier this month by Russian air strikes, even after the US military used emergency channels to ask Moscow to stop after the first strike, US officials say.
The rebel commander and the Observatory said the rebels had also captured an air base from Islamic State militants near Al-Bukamal. Heavy clashes were underway, with militants dug in at the Hamadan air base, 5 km northwest of Al-Bukamal.
The rebels also announced the capture of nearby Hamadan village. US-led coalition air strikes had hit militant hideouts in the town, the Observatory said.
Islamic State militants have cut power and communications in Al-Bukamal and dug trenches around the town, rebel sources say.
The rebel force, numbering several hundred, had secured the desert approaches to Al-Bukamal after a rapid advance across sparsely inhabited desert from al Tanf.
A US Defense Department spokesman, Major Adrian J.T. Rankine-Galloway declined on Tuesday to comment on the latest campaign but said Washington was assisting unnamed Syrian rebel groups.