At least three US Marines have been killed in an air crash near Darwin at Australia's northern seaboard, according to a statement.
The Marine Rotational Force (MRF) statement said the MV-22B Osprey tiltrotor military aircraft involved in the accident was "transporting troops during a routine training exercise".
"The Marines aboard the aircraft were flying in support of Exercise Predators Run. Recovery efforts are ongoing," the MRF statement said.
It disclosed that 23 US Marines were aboard the aircraft at the time of the accident.
At least five Marines have been transported to hospital in a "serious condition", the US statement said.
The US MRF said that the cause of the incident remained under "investigation".
Meanwhile, Australian media reports suggested that all the 20 surviving Marines sustained injuries during the incident.
Australian media reported that nearly 2,500 personnel from Australia, the US, the Philippines, Indonesia and East Timor were taking part in the drills.
US Military Presence in Australia
Nearly 2,500 US Marines are stationed in Darwin, the capital of Australia’s Northern Territory, under the 'Force Posture Initiatives' between the two treaty allies, according to an Australian government statement.
The first batch of nearly 200 US Marines were deployed in Australia in 2011 after an agreement between then Australian Prime Minister Julia Gillard and ex-US President Barack Obama.
The US military deployment has continuously expanded since then, with both the governments agreeing last month during AUSMIN talks that more American military personnel would be stationed at critical Australian military installations in coming years.