JIDDAH, Saudi Arabia — Key Arab allies promised Thursday to “do their share” to fight Islamic State militants, but NATO member Turkey refused to join in, signaling the struggle the U.S. faces in trying to get front-line nations to put aside their regional animosities and work together to defeat a common enemy.

The Arab states’ endorsement of a broad strategy to stop the flow of fighters and funding to the insurgents, and possibly to join military action, came as the CIA doubled its assessment of how many fighters the extremist group can muster.

Both Republicans and Democrats in Congress lined up Thursday behind President Barack Obama’s call to combat the militants, a day after he laid out a long-term campaign that would include expanding airstrikes against the fighters in Iraq, launching strikes against them in Syria for the first time and bolstering the Iraqi military and moderate Syrian rebels to allow them to reclaim territory from the militants.

The 10 Mideast allies announced their backing for a strategy to “destroy” the group “wherever it is, including in both Iraq and Syria,” following a meeting with U.S. Secretary of State John Kerry in the Red Sea coastal city of Jiddah.

Kerry’s visit, on the anniversary of the Sept. 11 attacks, was aimed at pinning down how much support regional allies are willing to give to the U.S. plan to beat back the Islamic State group, which has seized large chunks of Iraq and Syria. Nearly 40 nations have agreed to contribute to what Kerry said would be a worldwide fight to defeat the militants.

In remarks to reporters after the meeting, Kerry noted the “particularly poignant day” for the discussions.

“The devastating consequences of extremist hate remain fresh in the minds of all Americans, and to so many of our friends and allies around the world,” Kerry said of the terror attacks on the U.S. 13 years ago. “Those consequences are felt every day here in the Middle East.”