US Defence Secretary Chuck Hagel has ordered the first group of about 100 US troops to head to the Middle East in the next few days to establish training sites for Syrian opposition fighters battling Islamic State militants, the Pentagon said on Friday.

Admiral John Kirby, the Pentagon press secretary, said the troops, mostly special operations forces, were authorized last week and would begin arriving in countries outside Syria in the coming days, with a subsequent wave of several hundred military trainers following in the weeks thereafter.

The US focus in the campaign against Islamic State has been mainly on Iraq, with the exception of a large number of air strikes to support Kurdish fighters trying to prevent the takeover of the Syrian town of Kobani near the Turkish border.

Kirby said on Friday that Kurdish forces now control about 70 per cent of Kobani, which was seen a few months ago as being near collapse, with much of it in the hands of Islamic State.

He said the advanced element of US forces headed to establish training sites amounted to fewer than 100 troops.

"They're going to ... take a look at what's there and prepare for further deployments," Kirby said.

Turkey, Qatar and Saudi Arabia have offered to host sites where US forces could train members of the Syrian opposition to fight Islamic State and provide security in their home communities. Kirby did not say where exactly the first training sites were located.

The US military has said it is planning to send more than 400 troops for the training mission and several hundred support forces for a total of about 1,000 or more.

Kirby said last week that several hundred foreign military troops were also expected to act as trainers, including forces from the host countries.

He said on Friday that active recruitment of Syrian trainees had not started, although US military officials have been discussing the matter with Syrian groups.

Kirby said Major General Michael Nagata, the special forces chief tapped to handle the training mission, has had "very productive" meetings with Syrian opposition leaders.

"But it didn't lead to specific people signing up yet," Kirby added.

US officials have said if the current momentum continues, training could begin in the spring, with the first trainees returning to Syria at year's end. Officials plan to train 5,000 Syrian fighters a year for three years.-Reuters