IS repels SDF from east Syria holdout: monitor

Dozens of fighters Kurdish and Arab forces were killed after the Islamic State group pushed back the US-backed coalition from its holdout in eastern Syria, a monitoring group said on Sunday.

The Syrian Democratic Forces lost 72 fighters after IS took advantage of a storm that hampered coalition air cover and dispatched suicide bombers as part of their fightback, the Britain-based Syrian Observatory for Human Rights said.

An SDF commander told AFP that his forces had faced a "strong dust storm" and lacked local knowledge of the terrain, forcing them to retreat from the Hajin pocket near the Iraqi border seven weeks into an offensive.

Unlike IS, "our forces don't know the area and can't move around in conditions of zero visibility," the anonymous commander said.

"Military reinforcements and heavy weapons have been sent to the front and some units will be replaced by more experienced ones," the commander said.

"We will launch a new military campaign as soon as those reinforcements have arrived," he said.

The SDF, who are backed by airstrikes of the US-led coalition, launched its campaign to retake the IS holdout on September 10.

But they have faced a fierce fightback from the militants, including under the cover of sandstorms, the Britain-based Syrian Observatory for Human Rights says.

"In counterattacks since Friday to Sunday dawn, IS has taken back all positions to which the SDF had advanced inside the Hajin pocket," the monitoring group's chief Rami Abdel Rahman said.

More than 300 SDF fighters and around 500 IS jihadists have been killed in the past seven weeks of fighting, the Observatory says.

The coalition estimates that 2,000 IS fighters remain in the Hajin area.

IS overran large swathes of Syria and neighbouring Iraq in 2014, proclaiming a "caliphate" across land it controlled.

But the jihadist group has since lost most of that territory to various offensives in both countries.

In Syria, its presence has been reduced to parts of the vast Badia desert also in the east and the Hajin pocket.

A total of more than 360,000 people have been killed since Syria's war erupted in 2011 with the brutal repression of anti-government protests.