Syria: Washington sending 200 more soldiers for anti-IS push

Some 200 US troops will be sent to Syria to help an alliance of Kurdish and Arab fighters seize the Islamic State group bastion of Raqaa, Defence Secretary Ashton Carter said on Saturday.

The new batch of fighters will complement 300 American special forces already in Syria to assist US-backed Kurdish-Arab fighters who in recent weeks began their offensive on Raqqa.

"I can tell you today that the United States will deploy approximately 200 additional US forces in Syria," Carter told Gulf policymakers in the Bahraini capital Manama.

Carter told the Manama Dialogue security forum that the troop reinforcements will include bomb disposal experts and trainers as well as special forces.

Car bombs and elaborate networks of booby traps and mines have been the militants' favoured weapons as they battle to defend what remains of the "caliphate" they declared across Iraq and Syria in 2012.

"We're now helping tens of thousands of local Syrian forces to isolate Raqa," from which they are only about 25 kilometres (15 miles), he said.

Raqqa, which has also served as a hub for militants plotting attacks abroad, is being isolated according to plan, Carter said.

That operation coincides with a US-backed Iraqi effort to retake Mosul.

The two cities are the last major urban centres under IS control after the militants suffered a string of territorial losses in Iraq and Syria over the past year.

With the offensives against Mosul and Raqqa, the US-led coalition against IS has reached "a critical milestone", Carter said.

Iraqi forces are battling militants deep inside Mosul, edging closer to the River Tigris that divides the city and looking for a breakthrough in the seven-week-old offensive.

"This is a complex mission that will take time to accomplish but I'm confident that ISIL's days in Mosul are numbered," Carter said, using an alternative acronym for the group.

He warned that it is unclear what form IS will take after its eventual defeat in Iraq and Syria, so the coalition of Western and Middle Eastern nations battling it will need to remain vigilant.

"We must be ready for anything," said Carter, who is on a Middle East tour before leaving office at the end of President Barack Obama's term in January.

Meanwhile,  government warplanes have been pounding the remaining rebel-held districts of Aleppo as US officials prepared to meet with their Russian counterparts on Saturday in a last-ditch bid to prevent a bloodbath.

Secretary of State John Kerry said that the talks in Switzerland would try to stop Aleppo "being absolutely, completely destroyed".