BRUSSELS (AP) — U.S. Defense Secretary Ash Carter predicted on Thursday that recent U.S.-led efforts to accelerate the fight against the Islamic State group would produce "tangible gains" in Iraq and Syria by March, even as coalition partners pledged to expand and deepen their military contributions.

Carter said defense ministers from more than two dozen countries gave a "broad endorsement" of a refined U.S. plan for defeating the militants. After a meeting at NATO headquarters, Carter told reporters that nearly all participants either promised new military commitments or said their governments would consider new contributions.

"I'm very pleased that so many nations have stepped up and answered the call, even in recent days," Carter said. "But my challenge to coalition members to accelerate our military campaign will not end today, any more than America's resolve to lead and make more contributions itself will end today. It will continue."

Carter offered few details on what the "tangible gains" might look like. He suggested some would involve attacks on Islamic State financing and propaganda messaging, as well as bolstering Iraqi forces for the planned battle to take back Mosul in the north.

He said that 60 percent of the coalition members have increased their contributions, and another one-third said they will seek authority from their governments to do more.

In public remarks at the start of the meeting with coalition members, Carter cast the talks as an historic effort to hasten the demise of IS, which has proved resilient in Iraq and Syria and is spreading to Afghanistan, Libya and elsewhere in the greater Middle East.

"This ministerial marks the beginning of a new stage in the coalition campaign to defeat ISIL," Carter said, using a common acronym for the militants. He suggested that countries not answering his call to do more may regret their choice when the struggle is over.

"We will all look back after victory and remember who participated in the fight," he said.

In Munich, Germany, U.S. Secretary of State John Kerry was trying on Thursday to find a way to halt what amounts to a parallel war in Syria. Five years of civil war have pitted President Bashar Assad's government, backed by Russia and Iran, against an array of weakened opposition groups, some supported by the United States.

During the coalition meeting, Carter laid out details of the U.S. plan and asked coalition partners to increase or broaden their assistance, either militarily or in other ways such as financial contributions. He said the U.S. military, acting on instructions by President Barack Obama last October, is accelerating military efforts, which have shown positive results with the recent recapture of the Iraqi city of Ramadi in Anbar province.

Carter said coalition military chiefs, including U.S. Joint Chiefs Chairman Gen. Joseph Dunford, would meet soon to discuss and evaluate the campaign, and that in mid-March the U.S. Central Command headquarters in Florida would convene a military conference to assess progress.

"By then, at the latest, we should begin to see tangible gains from those additional capabilities, from the ones the coalition is already bringing to bear," Carter said.

Carter said the U.S. is determined to accelerate the war campaign and recapture as soon as possible the Islamic State group's main strongholds — Raqqa in Syria and Mosul in Iraq.

At a separate news conference, NATO Secretary-General Jens Stoltenberg said the alliance agreed Thursday to deploy NATO airborne command and control aircraft in order to free up similar U.S. aircraft for the campaign in Syria and Iraq. Details were to be worked out.

"We are looking into how we can step up our effort" beyond that, Stoltenberg said, suggesting that no additional NATO military contributions are imminent.

In a further sign of the complications caused by Russia's entry into the war, U.S. Gen. Philip Breedlove, the top NATO commander in Europe, said Turkey stopped flying missions over Syria out of concern of prompting a confrontation with Russia. Moscow was angered by Turkey's shooting down last fall of a Russian fighter jet that Turkey said entered Turkish airspace near Syria.

"The tensions are still very high, and there is no sense in provoking at this time," Breedlove told reporters.

He said Russia has informed the U.S. that it has linked its formidable air defenses in Syria with those of the Syrian government, creating a stiff threat to outside air forces.

The West claims the majority of Russia's airstrikes are targeting moderate groups that are opposed to Assad and IS; Russia says it is supporting Assad's government as part of a counterterrorism campaign.

The air campaign in Syria and Iraq is advertised as a 13-nation undertaking, but U.S. warplanes have conducted most of the hits.

A few coalition countries have promised increased support:

—The Netherlands has carried out airstrikes in Iraq, and said on Jan. 29 it would expand its efforts to Syria.

—Saudi Arabia indicated last week it could send ground troops into Syria. It was not clear whether the offer was conditioned on U.S. ground forces participating. Carter was meeting his Saudi counterpart on Thursday.

—Canada announced on Monday that it will quit conducting airstrikes in Syria and Iraq by Feb. 22. But it will expand its contributions to training Kurdish and other local forces and provide more humanitarian and developmental aid. Canada will keep two surveillance planes in the region and conduct aerial refueling missions.

Over the course of a decade and a half of coalition warfare in Iraq and Afghanistan, U.S. officials frequently have found themselves pleading and cajoling with the Europeans to contribute more. European countries generally have responded with pledges to do just a little bit more.

Inevitably it has fallen to the U.S. military, with greater resources and a longer reach, to carry the biggest burden in countering terrorism.

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