North Korea has reportedly detained a US citizen, bringing the total number of Americans held by them to three.

The man had been in the country for a month to discuss relief activities.

He was arrested at Pyongyang International Airport as he was leaving.

Meanwhile, the US super-carrier Carl Vinson has started joint exercises with Japan's navy.

It follows days of contention over where it actually was.

Washington has sought to clarify the aircraft carrier's whereabouts in recent days, after President Donald Trump suggested it was steaming towards North Korea.

It was in fact heading to Australia.