Iraq's request to the U.S.-led coalition for airstrikes in the campaign to retake Tikrit from Islamic State insurgents is "imminent," a senior diplomat from a Western nation that is part of the coalition said Tuesday.

If the coalition accepts the request, it would see by far the biggest collaboration so far against the militants by Iraqi forces, the Iranian-backed paramilitary forces and their Iranian advisers on the ground, and the United States and its allies.

There was no immediate confirmation from the Iraq government about the request, which the diplomat said would be positively received.