PARIS (Reuters) - The United States on Tuesday made its strongest indication yet that the battle to retake the Syrian city of Raqqa from Islamic State could be fast approaching, saying it would “overlap” with an already unfolding assault in Iraq to seize the city of Mosul.

Iraqi special forces soldiers looks at a destroyed Islamic State vehicle in a village near Mosul, Iraq October 25, 2016. REUTERS/Goran Tomasevic

Defense Secretary Ash Carter, speaking to reporters after meeting allies in Paris, did not disclose the timing of the Raqqa campaign but said preparations were on track.

“Yes, there will be overlap (in the Mosul and Raqqa campaigns) and that’s part of our plan and we are prepared for that,” Carter said after a gathering of 13 countries in the U.S.-led coalition fighting Islamic State.

His French counterpart, Defence Minister Jean-Yves Le Drian, also said preparations were on schedule.

Mosul, a city of 1.5 million people, and the smaller Syrian city of Raqqa are the two pillars of Islamic State’s self-declared caliphate, and recapturing them would be a pivotal defeat for the ultra-hardline Sunni jihadists.

U.S. officials acknowledge the Mosul campaign could take weeks or months, giving military planners time if they want both campaigns to run concurrently at some point.

A senior U.S. military official, speaking to reporters traveling with Carter, suggested the Raqqa kick-off would likely follow some additional successes in Mosul.

The official also said military planners would seek to avoid overstretching U.S.-led coalition assistance, which includes air strikes.

“I think everything is trending positively, (and) that we should be able to commence that effort some time in the near future,” the official said. “And again, I can’t even ballpark ‘near future’ right now but it’s imminent.”

Like in Mosul, where fighting on the ninth day of the offensive is still outside the city itself, the battle for Raqqa would also commence far from the center, likely relying on a mix of largely Kurdish and Arab fighters to battle Islamic State.

Arab forces are expected to be the ones to take the city itself, U.S. officials say.

“Truthfully, the Kurds that I’ve dealt with don’t intend – they’re not comfortable going into Raqqa. They know they can play a role in shaping and isolating Raqqa but it’s not their intent to be involved in the actual seizure of the city,” the U.S. military official said.

FOREIGN FIGHTER FLOWS

Islamic State itself is expected to morph into a more classic insurgency once it loses its final pockets of territory in Iraq and could lash out abroad with renewed attacks against Western targets, officials caution.

French President Francois Hollande, addressing the meeting, said the offensive on Mosul could trigger an outflow of foreign fighters - a concern for European nations wary of attacks by Islamic State militants returning from Iraq and Syria.

“We must also be very vigilant towards the return of foreign fighters,” Hollande said.

The gathering came just weeks before the first anniversary of attacks in Paris last Nov. 13 by Islamic State that killed 130 people. It was followed by other incidents in the United States and Europe perpetrated or inspired by the group.

Speaking on Sunday in Iraq, the top American commander of the U.S.-led coalition, Army Lieutenant General Stephen Townsend, said the United States had already sowed “a lot of confusion” among Islamic State’s fighters in Mosul by targeting its mid-tier leaders.

Carter on Tuesday said more than 35 Islamic State commanders were targeted by the coalition in the past 90 days.

The U.S. military official who briefed reporters with Carter said most of Islamic State’s external plots are still likely being hatched from Raqqa, as opposed to Mosul.

Hollande warned the coalition needed to watch out for flows of Islamic State fighters from one besieged city to another.

“In these columns of people leaving Mosul will be hiding terrorists who will try to go further, to Raqqa in particular,” Hollande said, calling for greater intelligence sharing.