By Tulay Karadeniz

ANKARA (Reuters) - Relying on a Kurdish militia in a U.S.-backed offensive to take the Syrian city of Raqqa from Islamic State could trigger prolonged ethnic conflict and Arab fighters should instead form the core of the operation, a senior Turkish official said.

At a briefing in Ankara, the official said planned offensives in Raqqa and the Iraqi city of Mosul, both Islamic State strongholds, should avoid causing further polarization in nations already grappling with bitter sectarian divisions.

"Raqqa is an Arab city with a million people. If you carry out an operation to this city with 7,000-8,000 Kurdish forces, you would trigger a sectarian battle," the official said. "That conflict would enflame all our border region."

Turkey also views the Syrian Kurdish YPG militia as a hostile force, an extension of Kurdish militants waging an insurgency on Turkish soil, putting it at odds with Washington, which sees the YPG as a valuable ally in the fight against Islamic State.

An operation is expected, possibly within weeks, to dislodge Islamic State militants from Mosul, Iraq's second-largest city, which fell to Islamic State in June 2014.

Turkey, which launched its first major military incursion into Syria last month to try to push Islamic State back from its border and stop Kurdish fighters gaining ground, has meanwhile been discussing a planned operation in Raqqa with the United States, officials have said.

However, President Tayyip Erdogan's spokesman said last week that Turkey would not take part in the Raqqa operation if it involved YPG fighters.

Talks between the militaries of Turkey and the United States had begun on the Raqqa offensive, the Turkish official said, declining to be identified so as to speak more freely. Details of the U.S.-led offensive to retake Iraqi city of Mosul were yet to be finalised, he said.


YPG fighters had yet to fully withdraw from Manbij, west of the Euphrates river, after a U.S.-backed operation to free the city from Islamic State earlier this year, the official said.

Turkey has said the Euphrates is a red line across which it does not want the YPG to come further west, fearing the Kurdish militia would then be able to join up cantons it already controls and seize a whole strip of territory on its border.

Ankara wanted to see Manbij jointly administered by Arab elements within the U.S.-backed Syrian Democratic Forces (SDF), which are dominated by the YPG, and the rebel Free Syrian Army, the official said. A similar force should work together in any Raqqa offensive, he said.

Driving out Islamic State from the Syrian city of al-Bab was among the targets of Turkey's incursion into northern Syria, the official said, but added that it would be a mistake in terms of military strategy to rush the campaign.

(Reporting by Tulay Karadeniz; Writing by Humeyra Pamuk; Editing by Nick Tattersall)