CANBERRA -- An emergency rescue operation is underway after a US military aircraft crashed off the coast of Australia's Northern Territory.

The Boeing V-22 Osprey was participating in a training exercise at 9:43 am local time on Sunday when it went down on Melville Island, approximately 60 km north of Darwin.

According to the Australian Associated Press, there were 23 personnel on board at the time of the crash.

As of Sunday afternoon, there had been no confirmed fatalities, but the Australian Broadcasting Corporation reported air medical service CareFlight transported three injured passengers, one of whom was in critical condition, to the Royal Darwin Hospital.

In a statement, Australia's Department of Defence said that all personnel on board the aircraft were Americans.

"Initial reports suggest the incident involves US defence personnel and that Australian Defence Force members were not involved," a spokesperson said.

"At this critical early stage, our focus is on the incident response and ensuring the safety of those involved."

More than 2,000 troops are participating in the annual Predator's Run training exercises in the Tiwi Islands.