(CNN) Two Marine pilots died in a helicopter crash near Yuma, Arizona, on Saturday, according to the US Marine Corps.

The two pilots were conducting a routine training mission when the AH-1Z Viper helicopter crashed around 8:45 p.m. PT. The cause of the crash is under investigation, according to a release from the Marine Corps. The pilots' names are being withheld until 24 hours after next-of-kin notification, according to the statement.