REUTERS - The U.S.-led coalition has inflicted serious damage on ISIS, carrying out around 1,000 air strikes so far in Iraq and Syria, but the fight against the militants could last years, U.S. Secretary of State John Kerry said on Wednesday.

The United States and its allies began air strikes against Islamic State after the Sunni militants made large territorial advances last summer. The Iraqi army, Sunni tribal fighters and Kurdish forces have since recovered some ground against them.

"Our commitment will be measured most likely in years but our efforts are already having a significant impact," Kerry said at the start of a first meeting of ministers from a coalition of more than 60 countries that Washington has assembled to destroy Islamic State, which is also known as Daesh.

"The roughly 1,000 coalition air missions we have flown have reduced Daesh's leadership and inflicted damage on its logistical and operational capabilities."

Kerry said Islamic State's momentum in Iraq had dissipated and Iraqi forces had retaken territory around Mosul and in Tikrit and had expanded security around some oil refineries.

In northern and western Iraq, Kurdish troops are battling Islamic State, while Sunni tribal fighters are "beginning to come on board," Kerry added.

In Syria, he said Islamic State command facilities had been destroyed, oil infrastructure damaged and a siege of the border town of Kobani blocked.

"It is much harder now than when we started for Daesh to assemble forces in strength, to travel in convoys and to launch concerted attacks," Kerry said. "No large Daesh unit can move forward aggressively without worrying what will come down on it from the skies."

The U.S.-chaired meeting was held at NATO headquarters in Brussels, but Kerry stressed it was not a NATO event.

Washington wants to discuss political coordination among coalition members but otherwise officials have been vague about the aims of the meeting.

Kerry praised the role of Arab states in the fight against Islamic State. Apart from Iraq, the meeting included representatives from Kuwait, Bahrain and Morocco.

Kerry, who held talks with Iraqi Prime Minister Haider al-Abadi before the meeting, also hailed "the significant progress" the new Baghdad government was making to implement a national program and to unite against Islamic State.

Kerry cited Baghdad's agreement this week with Kurds on oil exports and revenue and its order for the release of detainees held without formal charges.