US soldiers withdrawing from Syria 'within weeks' despite IS resurgence risk

American soldiers deployed to fight the Islamic State group return home within weeks, a top US army commander has said, following the shock announcement by President Donald Trump in December of a troop withdrawal.

Around 2,000 US troops are expected to be withdrawn from Syria in the coming weeks, a move that has shocked allies and led to the resignations of Defence Secretary Jim Mattis and other senior military officials.

The new announcememt was made by General Joseph Votel, the US CENTCOM chief overseeing American forces in the Middle East, but he cautioned that the exact timing still depended on the situation in Syria.

"Probably weeks. But again, it will all be driven by the situation on the ground," Votel said in response to a question about the date of the withdrawal.

"I think we're right on track with where we wanted to be... Moving people is easier than moving equipment and so what we’re trying to do right now is again (to) kind of clear out those materials, that equipment, that we do not need," he told reporters, according to Reuters.

The US military has already started withdrawing some equipment from Syria, but American troops are still providing support  for Syrian fighters battling the last remnants of the IS group in the country.

Fierce fighting was underway on Monday between US-backed Syrian forces and IS around the extremists' last foothold in eastern Syria.

The besieged militants are fighting back using suicide car bombs, snipers and booby traps, a Syrian war monitor and a Kurdish news agency said.

The US-backed Syrian Democratic Forces (SDF) on Saturday launched a final push to clear the area from IS under the cover of airstrikes by the US-backed coalition.

The capture of the IS-held village of Baghouz and nearby areas would mark the end of a four-year global war to end IS' territorial hold over large parts of Syria and Iraq, where the group established its self-proclaimed "caliphate" in 2014.

The Syrian Observatory for Human Rights said the push by the Kurdish-led SDF has been slow due to land mines and sniper fire, as well as the extremists' use of tunnels and suicide car bombs. The IS also using civilians as human shields, the Observatory said.

On Monday, the Observatory said 13 IS militants, including five suicide attackers, were killed in fighting, as well as six SDF fighters. The Kurdish Hawar news agency also reported heavy fighting Monday in Baghouz.

IS said in a statement posted late on Sunday that two of its "martyrdom-seekers" attacked SDF fighters in Baghouz with their explosive-laden car.

Syrian state media claimed a US-led coalition airstrike near Baghouz killed two women and two children.

More than 20,000 civilians have left the IS-held area in recent weeks.

US officials have said in recent weeks that IS has lost 99.5 percent of its territory and is holding onto fewer than 5 square kilometres in Syria (less than 2 square miles), where the bulk of the fighters are concentrated.

But activists and residents say IS still has sleeper cells in Syria and Iraq, and is laying the groundwork for an insurgency.

The US military has warned the group could stage a comeback if the military and counter-terrorism pressure on it is eased.

"They are dispersed and disaggregated, but there is leadership, there are fighters there, there are facilitators there," Gen Votel said. 

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