IP - The US Army has grounded all aircraft except those on "critical missions" on Friday a day after two Apache helicopters collided in Alaska, killing three US Army pilots.

Iran PressAmerica: The "aviation stand down" is effective immediately. It does not affect any other part of the US military besides the Army, US Chief of Staff James McConville said.

Before the Alaska collisions, a crash on 20 March involving two Black Hawk helicopters in Kentucky left nine soldiers dead.

James McConville said the aviators will remain grounded until they complete extra training.

He added Army pilots "will focus on safety and training protocols to ensure our pilots and crews have the knowledge, training, and awareness to safely complete their assigned mission".

The crash on Thursday occurred near Fort Wainwright, Alaska, as the troops were returning from a training mission, the Army said. In addition to the three that died, one was critically injured.

Three troops were part of the 11th Airborne Division, which is nicknamed the "Arctic Angels", according to the Associated Press.