A coalition of countries battling Islamic State jihadists in Syria and Iraq pledged Wednesday to pour more resources into the fight, after coming under strong pressure from Washington for greater contributions.

The promise came after a meeting in Stuttgart of defence ministers from countries involved in the anti-IS coalition, during which US Defence Secretary Ashton Carter drove home the message that to deal IS a body blow, "all must do more".

Carter's call to step up the fight came a week after US President Barack Obama reiterated a long-standing demand for members of NATO to increase their defence spending to meet the alliance's target of two percent of output.

In a joint statement, the coalition stressed their "strong support ... for the deployment of additional enabling capabilities in the near term, in order to hasten the collapse of ISIL's control" over the city of Mosul in Iraq and Syria's Raqqa.

Speaking after the talks with counterparts from Australia, Britain, Canada, Denmark, France, Germany, Italy, New Zealand, Norway and Spain, Carter said he was "confident that today's meeting will produce additional military commitments".

Besides military resources, defence ministers meeting at the US European Command's headquarters also examined their economic and political contributions to the campaign, he said.

"It's going to take more to win. We're going to win but we all need to do more," Carter told reporters.

"This fight is far from over and there are great risks," he said.

But "allowing ISIL safe haven would carry even greater risk. To accelerate ISIL's lasting defeat, all must do more," he said, using another acronym for the Islamic State group.

Carter also said he hoped that NATO as an organisation could join the coalition, particularly in the area of logistics coordination.

The defence secretary also pointed to "the NATO AWACS issue", in reference to surveillance aircraft of the alliance's members.

As a first step, NATO had agreed to deploy such surveillance aircraft, in order to allow the US to free up its planes for operations in Iraq and Syria.

But a diplomatic source said Washington is hoping to go a step further in getting NATO on board to fly such AWACS surveillance aircraft over Syrian and Iraqi airspace.

Carter also paid tribute to a US Navy SEAL who was killed in Iraq on Tuesday during an IS attack on a position of Kurdish peshmerga forces north of Mosul.

"The whole country has to be grateful to this young man and his family for this sacrifice. But tragically losses will occur.

"This is necessary to protect our country and not to do something would entail even greater risks," he said.

Carter said he had proposed that the anti-IS coalition hold another meeting in Washington this summer.