The Iraqi government provided a planeload of ammunition to fighters from Iraq's semiautonomous Kurdish region on Friday, a U.S. official said, in an "unprecedented" act of military cooperation between Kurdish and Iraqi forces brought on by an urgent militant threat.

The official said Iraqi security forces flew a C-130 cargo plane loaded with mostly small-arms ammunition to Irbil, the capital of Iraqi Kurdistan, in a bid to strengthen the region's peshmerga fighters as they struggle to keep militants from the Islamic State, an al-Qaida offshoot, at bay.

"This is unprecedented," the official said on condition of anonymity. "Developments over the last few days have refocused the issue, and we've seen unprecedented cooperation between Baghdad and Irbil in terms of going after (the Islamic State), not only in terms of conversation but in terms of actual support."