(Associated Press) — The U.S. Army says it has grounded aviation units for training after deadly helicopter crashes in Alaska and Kentucky killed 12 in the past month.

A U.S. Army team from Alabama has been making its way to the Alaska Interior to the investigate the midair collision between two AH-64 Apache helicopters. Three soldiers were killed and a fourth was injured Thursday.

Much is still not publicly known about the crash in the remote interior of the state that’s 250 miles from Anchorage. The AH-64 Apache helicopters were from Fort Wainwright, based near Fairbanks.

Thursday’s deadly crash follows a crash last month in Kentucky that killed nine.