US Secretary of State John Kerry on Wednesday hosts the first high-level meeting of the 60-member coalition trying to crush the Islamic State militant group in Iraq and in Syria.

Kerry, Iraqi Prime Minister Haider al-Abadi and foreign ministers from European, Arab and other countries will meet at NATO headquarters in Brussels to discuss the best military strategy against the group, officials said.

But they will also look at how to stem the flow of foreign fighters and delegitimise the powerful IS "brand," that has drawn jihadists from several Western countries, the officials added.

"This is the end of the beginning of the formation of the coalition. This is where the coalition comes together," a senior State Department official told reporters with Kerry.

The United States launched the first strikes against IS in Iraq in August. In late September the strikes were extended to IS targets in Syria, involving both the United States as well as a number of allies.

Saudi Arabia, the United Arab Emirates, Jordan and Bahrain are taking part in the air strikes in Syria and Australia, Belgium, Britain, Canada, Denmark, France and the Netherlands are participating in Iraq.

Separately, the Pentagon Tuesday confirmed for the first time that Iran recently carried out air strikes against IS in eastern Iraq.

The threat posed by IS has brought the two arch-foes together in the fight against the jihadists but Washington said the Iranian raids were not coordinated with US forces.

The United States has carried out the vast majority of the air strikes against the jihadists who proclaimed a caliphate in Syria and Iraq in June.

Dozens more countries are offering other support including information and intelligence sharing.

Kerry on Tuesday did not rule out providing more aid to the Iraqi government. "I'm confident that over a period of time the United States will be providing additional assistance of one kind or another," he said.

- Threat from foreign fighters -

Officials said the ministers will tackle how to disrupt IS finances and how to provide humanitarian aid to displaced people in Iraq and Syria.

The senior US official said the coalition partners are particularly concerned about the threat posed by thousands of foreign fighters who have joined IS and who could launch attacks in the West.

"It may be in fact one of the longest term problems that we'll ultimately face with respect to ISIS in this region," he said, using the group's alternate name.

Washington was working with European and Gulf Arab states about tightening borders and establishing no-travel lists, he added.

Coalition partners, he said, are due to meet in Marrakesh, Morocco on December 15 to further tackle the foreign fighters problem.

NATO has allowed its headquarters to be used for Tuesday's talks because foreign ministers from the transatlantic alliance met there on Tuesday, but NATO is not part of the US-led coalition against IS.

The ministers will discuss ways to send "counter-messages" to delegitimise IS, which has been savvy in using social media to recruit fighters and supporters over the Internet.

"As we are able to delegitimise (IS), we are able to turn populations against (IS), reduce their recruiting basis," he added.

The ministers will study ways to disrupt how IS raises finances through oil sales, extortion, plunder, ransom, human trafficking and the sale of Syrian antiquities, he said.

"We're working hard to map the oil system," he said, adding the coalition is tracking oil from the ground, to refineries, to black markets through tankers crossing borders, to the sources of cash and then banks.

Air strikes on refineries are undermining the IS ability to export the oil, and thereby raise funds, he said.

"We're just kicking off on many of these things. And what we're beginning to see already there is some effect that's beginning to become apparent."

The official said based on intelligence estimates there are around 30,000 IS fighters in both Syria and Iraq.