BRUSSELS - Defence ministers from the US-led coalition striking the Islamic State group met Thursday in a bid to engineer a decisive new phase in what has become a difficult fight with no end in sight.

Pentagon chief Ashton Carter convened the Brussels summit to persuade partner nations to contribute more to the campaign against the extremists, who despite 18 months of air strikes remain firmly in control of large parts of Iraq and Syria and have a growing foothold in Libya.

Further complicating the situation is Russia’s own air campaign in Syria, which Moscow insists is also targeting IS, but which the West says is in fact aimed at rebels opposed to President Bashar al-Assad.

“The fight to defeat ISIL should matter to all of us, and each contribution matters to this fight,” Carter said as he opened the meeting, using an alternative acronym for the IS group.

“ISIL’s activities are an affront to our common human dignity and to the common set of values that brings this diverse coalition of nations together.”

The summit marks the culmination of weeks of work for Carter, who has taken a two-pronged approach to winning broader support from coalition members.

While he has written to each one privately, he has also publicly accused some unspecified members of the 66-nation coalition of doing “nothing at all” to help the fight. A senior US defence official said Washington was looking not just for pledges of military support and cash, but ideas too.

“The secretary will, frankly, give a call to his fellow ministers to be creative, to speak up to contribute to the thought leadership in the campaign,” the official said, speaking on condition of anonymity. “There’s no monopoly on good ideas.”

The assessment comes after the coalition has carried out more than 10,000 air strikes in Iraq and Syria at a cost to the United States of nearly $6 billion (5.2 billion euros). The effort has dealt some significant blows to the militants: the Pentagon estimates IS has lost about 40 percent of the territory it once held in Iraq, and about 10 percent in Syria.

But despite losing control of the Iraqi city of Ramadi, assaults to recapture the key IS bastions of Mosul in Iraq and its self-proclaimed capital in Syria’s Raqa are still many months away, and thousands of IS fighters have streamed into Libya.

Carter’s efforts to solicit broader commitments have borne some fruit. Canada, for instance, announced Monday it would triple the number of special forces training Kurdish militia in northern Iraq to about 210.

And Slovenia has said it would start sending military trainers to work with local forces trying to push back IS.

“There are a number of other (countries) who are in the final throes of trying to figure out if they can also make that leap,” the official said, noting that several other nations are “very seriously” considering additional contributions, but first need parliamentary approval.

In all, 27 coalition members which have contributed militarily to the fight joined Carter’s delegation in Brussels while another 21 were attending as observers.

The summit came at the conclusion of a two-day meeting of Nato defence ministers that dealt with a range of separate issues.

Nato has until now had no official role in the anti-IS fight, although all of its 28 members play some part, and officials indicated the alliance could be increasingly called upon to help.

“There are lots of opportunities that are being considered,” Nato’s Supreme Allied Commander Europe Philip Breedlove said. “There now seems to be serious conversations about some possibilities of Nato actually being involved to some limited degree.”