WASHINGTON (Reuters) - Islamic State administrators and bureaucrats have started to flee the militant group’s Syrian stronghold of Raqqa as a U.S.-backed alliance works to isolate the city, a Pentagon official said on Friday.

“A lot of their administrators and bureaucrats now are beginning the process of leaving Raqqa and moving their operations further down river,” Pentagon spokesman Captain Jeff Davis told reporters.

“So they have definitely taken note of the fact that the end is near in Raqqa and we are seeing now an exodus of their leadership,” Davis said.

He did not specify how many Islamic State members were leaving or what exact roles they played, but said the withdrawal seemed to be organized and of their non-combatant “support people.”

A U.S.-backed alliance of Syrian Kurdish and Arab fighters also said on Friday it was launching new attacks against Islamic State, after capturing dozens of villages in the latest phase of a battle to weaken the jihadists in their Syrian strongholds.

The Syria Democratic Forces (SDF), which include Arab groups and the powerful Kurdish YPG militia, have for months been fighting Islamic State in northern Syria around its de facto capital Raqqa.

The SDF started a new phase of its campaign earlier this month, aiming to encircle Raqqa and sever the road to militant strongholds in Deir al-Zor province along the Euphrates River.

Islamic State is fighting separate battles against various sides in Syria’s multi-sided conflict: the SDF, backed by U.S. air power; the Syrian army and its allies, supported by Russian air power in Deir al-Zor and areas further west; and Syrian rebels backed by Turkey in areas of Aleppo province northwest of Raqqa.

The ultra-hardline jihadist group is 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 al-Zor city, most of which it controls, and capturing in December, for a second time in Syria’s conflict, the ancient city of Palmyra.