Defense Secretary Chuck Hagel has ordered the first group of about 100 U.S. 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.

Adm. John Kirby, the Pentagon's press secretary, said the troops, mostly special operations forces, were authorized a week ago 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 U.S. focus in the campaign against the Islamic State group has been mainly on Iraq, with the exception of a large number of airstrikes to support Kurdish fighters trying to prevent the takeover of the Syrian town of Kobani near the Turkish border.