US Secretary of State John Kerry has warned it will take years for a US-led coalition to defeat the Islamic State in Iraq and the Levant (ISIL), as Washington said arch-foe Iran had launched its first air strikes against the fighters.

Speaking at NATO headquarters in Brussels during the first high-level talks of a coalition of 60 nations fighting ISIL, Kerry said that strikes against the fighters were having a “significant” impact and vowed that they would stay the course.

“Our commitment will most likely be measured in years,” he said, adding: “Our efforts are already having a significant impact.”

Kerry told foreign ministers taking part in the talks that the coalition of Western and Arab states “will engage in this campaign for as long as it takes to prevail”.

His comment came hours after Pentagon said Iranian F-4 Phantom jets hit ISIL fighters in eastern Iraq in recent days but denied any military coordination with long-term adversary Iran. Tehran refused to confirm or deny any strikes.

Iran is not a member of the coalition, but the claim suggested a tacit understanding between Iran and the United States to tackle the common threat from a group that proclaimed a caliphate in Iraq and Syria in June.

Kerry made no comment on Iran, while Iraqi Prime Minister Haider al-Abadi, asked about the Iranian action, said he had “no knowledge of any Iranian air strikes”.

The United States launched its first strikes against ISIL in Iraq in August.

In late September the strikes were extended to ISIL targets in Syria, involving 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. Australia, Belgium, Britain, Canada, Denmark, France and the Netherlands are participating in Iraq.

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

The United States has carried out the vast majority of the air strikes against the self-declared jihadists.

It says there are around 30,000 ISIL fighters in both Syria and Iraq, where the group is accused of atrocities including rape, crucifixion and the beheading of several westerners. SAPA