The US Marine Corps may ground its entire air fleet for a safety review following the crash of an Osprey tilt-rotor aircraft in Australia that killed three Marines, a defense official said Monday.

The Japan-based Marine MV-22 Osprey crashed Saturday during an exercise off the Australian coast, leaving three service members missing and presumed dead.

"We are looking at our options in terms of reviewing safety across the Marine Corps fleet at the moment ... pending an across-the-board safety review," a US defense official told AFP, noting that the grounding could affect all flying squads in the service.

US officials are also weighing a request by Japan's new defense minister, who told the US military on Monday of his "many concerns" after it flew an Osprey in Japan following the crash.

Itsunori Onodera, appointed Thursday as Japan's defense minister, asked the US to temporarily stop flying the aircraft in his country following the accident.

According to the US official, the Osprey crashed after clipping the back of the USS Green Bay while trying to land on the amphibious transport ship. The Okinawa-based aircraft which crashed was in Australia as part of a joint military exercise called Talisman Sabre, which has just ended in Queensland state.

The commander of more than 80,000 US marines in the Pacific is urging Australia to join operations against Islamic State (IS) militants in South-East Asia.

Lieutenant General David Berger is visiting Australia to check on readiness for the Talisman Sabre military exercises off the Queensland and Northern Territory coasts.

He told the ABC the "movement of violent extremist organisations" was a "very real problem" for countries like the Philippines, Malaysia and Indonesia.

The Hawaii-based commanding general of US Marine Corps Forces Pacific said he expected Australian forces could soon join American personnel fighting Islamic extremists in this region.

"Both of us have a long history of being an expeditionary force when needed, so we begin from a common point I think and we've operated alongside for 100 years," General Berger said.

"Regionally where you're looking for stability, where you're looking to reassure other countries that there will be a strong enough force in the region to deter bad behaviour, I think absolutely yes — we would go where asked."

The visiting US general warned that Australia's neighbours would need assistance if they were to successfully stop the threat posed by IS-inspired militants. "I think the potential for it to spread is there, we should not underestimate it," he cautioned. "It's a different kind of a threat than North Korea but it's also a threat that moves in order to survive — it doesn't own a state so it's mobile.

INDONESIA has nothing to fear from the deployment of US Marines in the Territory, the Commanding Officer of the Marine Rotational Force Darwin said on Tuesday.

Lieutenant Colonel Brian S. Middleton had just landed with the first 200 of 1250 US marines who will form the sixth and most complex US marine air ground taskforce to be deployed to the Territory.

Although reluctant to comment on the issue, Lt-Colonel Middleton said he was aware of comments made by Indonesia’s armed forces chief Gatot Nurmantyo in January questioning the US marine presence in Darwin.

General Nurmantyo said while pretending to be on a visit to Darwin he spent 90 minutes on the harbour looking at US marine facilities.

“I saw two landing bases had already been built. Even though Australia is a continental state — what does it need marines for?” he told Indonesian media.

The Indonesian general has previously criticised Australia’s hosting of US marines.

“I am aware of his comments … Indonesia has nothing to fear from US marine deployments to Darwin,” he said. “The US alliance with Australia remains strong and we know why we are here. That is for US Marines and Aussie Diggers to train and operate alongside each other.”

It is believed General Gatot Nurmantyo has political ambitions and Lt-Colonel Middleton agreed that the General’s comments were probably aimed at local consumption. However, he pulled no punches when asked about the role the 1250-strong marine air ground taskforce deployment would play if tensions between his country and North Korea escalated into direct conflict.

Lieutenant Colonel Brian S. Middleton, says the 1250 US Marine deployment to Darwin stands ready to fight if tensions between his country and North Korea escalate into direct conflict.

Lieut. Colonel Middleton said when US Marines were in forward deployment they were ready for battle.

Lieut. Colonel Middleton is leading the sixth and most complex US marine air-ground task force to be deployed to the Territory.

Along with the 1250 marines that make up the latest Darwin rotation of US troops, it will eventually include up to 13 aircraft, four tilt-rotor Ospreys, five Super Cobra helicopters and four Huey helicopters.

When asked about the North Korea stand-off he said: “We stand ready to fight.”

The marines are from 3rd Battalion, 4th Marine Regiment from Camp Pendleton, California. They will be based at Robertson Barracks, RAAF Base Darwin and Defence Establishment Berrimah.

Marine Rotational Force Darwin is mainly a series of joint exercises, training and exchanges between the US and the Australian Defence Force, but some exercises will also involve military personnel from China and other Asian countries.

The US has rotated a small force of Marines through Darwin since 2012. It was originally planned to send a full Marine Air-Ground Task Force of 2500 Marines to Australia by 2016, but the timeline has been pushed back to around 2020.

More than 1,000 US marines begin arriving in the Top End and say they are ready for whatever may happen as North Korea escalates its nuclear threat.

The first group of 1,250 marines touched down in Darwin on Tuesday morning for their sixth annual dry season rotation in the Top End.

Their arrival comes as Foreign Minister Julie Bishop defended US President Donald Trump's "they gotta behave" message to North Korean leadership after its failed missile test on Sunday.

"[North Korea] is on a path to achieving nuclear weapons capability and we believe Kim Jong-un has a clear ambition to develop an intercontinental ballistic missile capable of carrying a nuclear payload as far as the US," Ms Bishop said.

"That would mean Australia would be in reach so unless it is prevented from doing so, it will be a serious threat to the peace and stability of our region, and that is unacceptable."

In Darwin, the rotation's commanding officer Lieutenant Colonel Brian Middleton said the force was ready, come what may.

"Any time a marine force is forward deployed, we are always on standby for anything," he said.
He said this year's contingent was "the most robust package" the marines had put together for training in the Top End, featuring an "ace aviation combat element" of 13 aircraft.

Over the next two weeks, the deployment's largest fleet of military aircraft yet will be brought to Australia as part of the agreement, including four high-speed troop transporters, the MV-22 Osprey, five Super Cobra helicopters and four Huey helicopters. The next six months will see the troops train with their Australian counterparts and other nations, including Japan and China.