Syrian rebels close in on strategic IS group-held city

Syrian rebels advancing on Islamic State group fighters in the strategic northern city of Manbij have seized more than 100 square kilometres this week, the US military has said.

US Central Command spokesman Colonel Patrick Ryder said yesterday that more than 55 air strikes have been conducted since the offencive began on Monday, and that the rebel forces had secured areas on the western bank of the Euphrates River.

"They are facing some heavy resistance from ISIL, which was expected" but "are continuing to move forward," he added, using an acronym for the IS group.

Manbij is located along a route connecting Raqa— the IS group's de facto capital— to the Turkish border, a vital conduit for supplies.

A rebel victory would inflict one of the largest strategic defeats on the IS group since it proclaimed its rule over territory in Iraq and Syria two years ago.

Retaking Manbij would "cut this key route to prevent ISIL from using it to move fighters, weapons, finances, supplies into and out of Syria and Iraq," Ryder said.

Some 3,000 local Arab fighters are taking part in the offencive, backed by around 500 Kurdish militia members.

"They are from this area, they are liberating their hometown," Ryder said.

US special forces are also working "at the command and control level" in the operation, he added.

The United States has sought to mobilise Arab groups in the ground offencive against the IS group since the launch of the US-led coalition campaign in September 2014.

With little success so far, a victory for Arab rebels in Manbij would provide welcome news for the White House.