BRUSSELS -- U.S. Defence Secretary Ash Carter said Thursday he expects a gathering of more than two dozen countries contributing to the war against the Islamic State in Syria and Iraq to endorse a U.S. plan for accelerating the campaign.

"That will be new, for there to be a plan that everyone sees, which is a concrete military campaign plan and an opportunity to do what the United States has been doing for some months now, which is accelerating its own contributions," Carter told reporters in advance of convening an anti-IS meeting of some two dozen defence ministers.

Speaking at NATO headquarters, Carter said he would lay out details of the campaign plan in an afternoon meeting with allies and non-NATO partners such as Saudi Arabia and Iraq. In doing so, he will ask the others to find ways to increase or broaden their contributions -- either militarily or in other ways such as financial contributions.

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

Later 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 air campaign in Syria and Iraq. He said details were to be worked out later.

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

A few coalition countries have made promises of increased support in recent days. The Netherlands, which has been carrying out airstrikes in Iraq, said on Jan. 29 that it would expand its efforts to Syria. Saudi Arabia indicated last week it could send ground troops into Syria, although it was not clear whether the offer was conditioned on U.S. ground forces participating.

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

Carter said some countries whose defence ministers may say during the Brussels meeting that they intend to contribute more will be unable to make formal, specific commitments because their governments require parliamentary approval of such military moves.

"We will array all of the capabilities that will be required to carry out this plan," Carter said. In doing so, he said, he will be pointing to combat, training and other contributions that allied countries "may not yet have realized that they could make and that are going to be necessary" to succeed.

On the sidelines of Thursday's meeting, Carter was scheduled to hold a one-on-one meeting with Saudi Arabia's defence minister, Mohammed bin Sultan. Aides indicated that Carter hoped to learn more details about the Saudi proposal to deploy ground troops to Syria, an offer that the Obama administration has welcomed.

Over the course of a decade and a half of coalition warfare in Iraq and Afghanistan, U.S. officials have frequently found themselves pleading and cajoling with the Europeans to contribute more, and they generally have responded with pledges to do just a little bit more. The pattern may be repeated in Brussels. Inevitably it falls to the U.S. military, with greater resources and a longer reach, to carry the biggest burden in countering terrorism.

The air campaign in Syria and Iraq, for example, is advertised as a 13-nation undertaking. But of the 10,060 strikes conducted over the past year and a half -- 6,723 in Iraq and 3,337 in Syria, as of Feb. 1 -- U.S. warplanes have conducted all but 2,124 of the Iraq hits and all but 208 in Syria. At their low point last August, the allies conducted only two strikes in Syria while the U.S. conducted 210, according to figures provided by the Pentagon. More recently, non-U.S. airstrikes have increased as a share of total strikes.