U.S. aircraft killed more than 20 Al Qaeda fighters who opened fire on an American air patrol northwest of Baghdad, the military reported on Sunday.

The firefight between the U.S. aircraft and the insurgent fighters occurred Saturday about 28 kilometers (17 miles) northwest of the capital, the statement said.

"Patrolling the skies, aircraft from the 1st Air Cavalry Brigade, 1st Cavalry Division had reported to the scene to observe possible extremist activities in the area based off of a report from local Iraqi security volunteers that an Al Qaeda cell was working in the area," the military said.

"The aircraft observed about 25 Al Qaeda personnel carrying AK-47 assault rifles, with one of the men brandishing an RPG (rocket-propelled grenade), and walking through an area of local shops and into a palm grove. Shortly after spotting the men, the aircraft were fired upon by the insurgent fighters," according to the statement.

The military did not say what kind of aircraft were involved but the fact that the fighters opened fire suggests they were low-flying Apache helicopters.

Four vehicles were destroyed and no Iraqi civilians or U.S. soldiers were killed or wounded, the military said.

Iraq's Defense Ministry, meanwhile, said Iraqi soldiers had killed 42 "terrorists" over the past 24 hours. The operations were centered in Salahuddin and Diyala provinces and around the city of Kirkuk, where the ministry said its soldiers had killed 40 and arrested eight. It said 52 fighters were arrested altogether.