US troops inside Raqa, ISIL Syria stronghold: Official

United States military advisers are operating inside Raqqa, the Syria bastion of Islamic State of Iraq and the Levant (ISIL), a U.S. official has said.

The troops, many of them special operations forces, are working in an "advise, assist and accompany" role to support militans of the Syrian Democratic Forces (SDF) , said Colonel Ryan Dillon, a military spokesman. The People's Protection Units (YPG), which Turkey views as terrorist for its link to the outlawed Kurdistan Workers' Party (PKK) constitutes the backbone of the SDF. The U.S. troops are not in a combat role but are calling in air strikes and are working closer to the fight than did U.S. forces supporting the Iraqi military in Mosul.

"They are much more exposed to enemy contact than those in Iraq," Dillon said.

He said the numbers of U.S. forces in Raqqa were "not hundreds" and that they had been working closely with SDF fighters since operations to encircle Raqa began.

After months of capturing villages and surrounding terrain, operations to liberate Raqa started in November and on June 6 the SDF entered the city.

With help from the U.S.-led coalition, the SDF this month breeched an ancient wall by Raqa's Old City, where diehard jihadists are making a last stand.

The SDF are a Kurdish-Arab alliance that is being trained by coalition experts and armed by the United States.

Dillon said the coalition had seen IS increasingly using commercial drones that have been rigged with explosives. The jihadists employed a similar tactic in Mosul.

"Over the course of the last week or two, it has increased as we've continued to push in closer inside of Raqa city center," he said.

The U.S. military is secretive about exactly how big its...