Three U.S. Marine Corps troops died Sunday after a military aircraft crashed near Darwin, Australia, during a routine training exercise.

The aircraft, an MV-22B Osprey, crashed on Melville Island while transporting troops about 9:30 a.m. local time with 23 personnel on board, the Marine Rotational Force said in a statement. Five others have been transported to Royal Darwin Hospital in serious condition.

The Marines were taking part in Exercise Predator Run, according to the statement, a joint military exercise also involving soldiers from the Philippines, Indonesia and Timor-Leste.

Recovery efforts are ongoing and an investigation into the cause of the crash is underway, the statement said.