Islamic State leaders flee Syria's Raqqa: Pentagon

Leaders of the Islamic State (IS) group are leaving their Syrian stronghold of Raqqa, fleeing the Arab-Kurd offensive backed by an international coalition, the US Defense Department said on Friday.

"We are starting to see now that a lot of senior ISIS leaders, a lot of their bureaucrats ... are beginning the process of leaving Raqqa," said Pentagon spokesman Navy Captain Jeff Davis, using an alternate acronym for the militant group.

"They have definitely taken note of the fact that the end is near in Raqqa," he told reporters, describing a retreat that seems "very organized, orderly".

After a string of major losses in both Iraq and Syria, the militant’s two main strongholds of Mosul and Raqqa are under attack from forces backed by the US-led coalition.

After a four-month campaign, Iraqi forces are tightening the noose on Mosul, while in Syria, the Arab-Kurd alliance, the Syrian Democratic Forces, has been advancing to cut off Raqqa.

According to the Pentagon spokesman, that objective is nearly complete, with IS now controlling only one road, in the southeast of the city.

Located along the north bank of the Euphrates River, the road links Raqqa to Deir Ezzor, said Davis, who did not give specific details about the extent of the militant group’s retreat.

Roads in the north and west are blocked by the Syrian Democratic Forces, and in the south, by the destruction of bridges over the Euphrates, he said.

While the isolation operation around Raqqa has made progress, the coalition has not announced its plan for recapturing the city.

IS is fighting separate battles against various sides in Syria's multi-sided conflict: the SDF, backed by US air power; the Syrian army and its allies, supported by Russian air power in Deir Ezzor and areas further west; and Syrian rebels backed by Turkey in areas of Aleppo province northwest of Raqqa.

The group is also under pressure in its last major Iraqi stronghold of Mosul, across the border.

But it has hit back in some areas, advancing on a Syrian government-held enclave in Deir Ezzor, most of which it controls, and capturing in December, for a second time in Syria, the ancient city of Palmyra.

Still unknown is what role the armed wing of the Kurdish Democratic Union Party, the YPG, will play in the US-backed Arab-Kurd alliance.

The YPG, considered a terrorist group by Turkey, fights IS in northern Syria as well as against Ankara's forces.

Turkish President Recep Tayyip Erdogan has proposed that the coalition replace the YPG with Turkish forces.

The new US defense secretary, James Mattis, met on Thursday with his Turkish counterpart Fikri Isik in Brussels.

Chairman of the US Joint Chiefs of Staff Joe Dunford is due to meet with the top Turkish military leader on Friday in Turkey, the Pentagon said.