In this photo released by the U.S. Army, AH-64D Apache Longbow attack helicopters from the 1st Attack Battalion, 25th Aviation Regiment, fly over a mountain range near Fort Wainwright, Alaska, on June 3, 2019.
CNN  — 

The chief of staff of the US Army has grounded all Army aviators not involved in critical missions following two recent helicopter crashes that left 12 soldiers dead.

The order from Army Chief of Staff James McConville grounds the aviators “until they complete the required training,” according to the Army.

“The safety of our aviators is our top priority, and this stand down is an important step to make certain we are doing everything possible to prevent accidents and protect our personnel,” McConville said in a statement.

Army pilots, at McConville’s direction, “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 safety stand down comes after Thursday’s mid-air collision of two AH-64 Apache helicopters near Fort Wainwright, Alaska, that killed three soldiers and wounded another. Two of the soldiers died at the scene and the third died while being transported to a hospital, according to a release from the US Army’s 11th Airborne Division.

The crash occurred about 100 miles south of Fort Wainwright, where the helicopters are based as part of the 1st Attack Battalion, 25th Aviation Regiment.

“This is an incredible loss for these soldiers’ families, their fellow soldiers, and for the division,” Maj. Gen. Brian Eifler, commanding general of the 11th Airborne Division, said in the release. “Our hearts and prayers go out to their families, friends and loved ones, and we are making the full resources of the Army available to support them.”

That deadly collision came just weeks after nine soldiers were killed when two HH-60 Black Hawk helicopters crashed during a nighttime training mission near Fort Campbell, Kentucky, the Army said.

The medical evacuation helicopters were conducting a routine training mission when they crashed at approximately 10:00 pm local time in an open field across from a residential area. All nine of the service members aboard the two aircraft were killed.

The incidents are under investigation, according to the Army, but “there is no indication of any pattern” between the two.

CNN’s Haley Britzky contributed to this report.