WASHINGTON - Two US soldiers were killed when their Apache helicopter crashed at Fort Campbell, located in the state of Kentucky, the army announced Saturday.

The crash involving an AH-64E Apache helicopter occurred during a routine training mission late Friday, according to a statement from the army's 101st Airborne Division.

The recovery operations are currently ongoing at the crash site and an investigation is underway.

The names of the two soldiers will not be released until their families are notified.

"This is a day of sadness for US Army Fort Campbell and the 101st Airborne Division," said Brigadier General Todd Royar, acting senior commander of the 101st Airborne Division and Fort Campbell. "Our thoughts and prayers are with families during this difficult time."

Friday's incident follows a series of military crashes involving US troops.

Four Marines died Tuesday in the crash of their CH-35E Super Stallion helicopter during a training flight in California.

A pilot of the air force's elite Thunderbird squad died Wednesday when his F-16 jet crashed near an air base outside Las Vegas as he was preparing for an air show.