Allies Pledge to Help U.S. Fight Islamic State

Extent of Cooperation in Military Operations Still Unclear.

John Kerry speaks with Saudi Arabia's Foreign Minister Prince Saud al-Faisal, right, at King Abdulaziz International Airport in Jeddah on Thursday.

A day after President Barack Obama outlined a strategy to combat Islamic State militants, Washington’s international allies didn’t make clear how far they would go to join military operations even as they pledged their support.

Mr. Obama vowed to “degrade and ultimately destroy” the extremist group which has grabbed territory across Iraq and Syria and harbors ambitions for more. After a day of consulting with Secretary of State John Kerry in Saudi Arabia, most of Iraq’s neighbors signed onto a statement of support.

In the communiqué, leading Arab states committed to working with the U.S. to cut off the flow of foreign fighters and funds into the Islamic State, Turkey—which has opposed allowing the U.S. to use bases on its territory for airstrikes against Islamic State—didn’t sign the communiqué. Nearly 50 Turkish diplomats are being held by militants in the Iraqi city of Mosul, which Islamic State captured in June.

In Europe, Germany said it wouldn’t take part in airstrikes, while the U.K. said it wasn’t ruling out participation. Several dozen European and other countries agreed during this month’s North Atlantic Treaty Organization summit in Wales to support the campaign, but as of Thursday, many were still weighing the specific nature of their involvement.

At the core of the emerging alliance, said U.S. and Arab officials, is an agreement with the Saudi government for it to host a training facility for thousands of Syrian rebel fighters who are combating both the Islamic State and President Bashar al-Assad’s regime. Administration officials said Wednesday the deal was in place, but said late Thursday talks were still ongoing.

Among other uncertainties, U.S. and Arab officials said discussions about Mideast governments providing basing and overflight rights to American warplanes are ongoing. Also unclear is whether any of the leading Arab states would join in U.S. airstrikes against militants in Iraq and Syria. Qatar and the United Arab Emirates joined in the 2011 air campaign in Libya that helped overthrow strongman Col. Moammar Gadhafi.

Adding urgency to the effort, the Central Intelligence Agency in a new estimate Thursday said the size of the militant group at least doubled over the summer. Islamic State “can muster” between 20,000 and 31,500 fighters, said agency spokesman Todd Ebitz, citing a new review of intelligence reports from May through August.

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