The 19-year-old marine, who was stationed in Japan, was among 300 US troops who had travelled to the northern capital of Darwin for air combat training.

He was named by the US Embassy as Lance Corporal Bryce Miller.

His body was found by a snorkeller at Wangi Falls in Litchfield National Park, south of here.

A police spokeswoman said Miller had gone to the swimming hole Saturday with a group of 10 servicemen but became separated from the others.

She said there were no suspicious circumstances surrounding his death.

Authorities were trying to contact Miller's US relatives to gain permission to perform an autopsy, the spokeswoman said.

US commanding officer Lieutenant Colonel Bruce Bright said the squad would continue with its two-month training mission but would take time out to respond to the tragedy.

"At 19 years old when you lose a friend they don't know what to think," Bright told Australian Broadcasting Corporation radio.

"I've spoken with them twice now and we're going to slow down just a bit for a couple of days.

"I've got my chaplain, we have a preacher here with us and then we have plenty of support within the squadron, with our staff and... officers."

WAR.WIRE