North Korea has lost one of its submarines, US officials have claimed.
Officials in the highly isolated Communist state apparently lost contact with the submarine - which is now presumed to have sunk, it was claimed.
The apparent loss came as the state's neighbour and foe South Korea conducted military drills together with the US just over the border.
There have been heightened tensions in the region stoked by the North's recent nuclear weapon tests.
American officials told CNN that they had been observing the North Korean submarine off the country's eastern coast when it vanished earlier this week.
Spy satellites had also seen watching the country's navy carry out a search, they said.
"The speculation is that it sank,” an American official told the US Naval Institute News website.
“The North Koreans have not made an attempt to indicate there is something wrong or that they require help or some type of assistance.”
It came as US and South Korean troops staged an large-scale amphibious landing exercise on Saturday.
The allies stormed mocked-up North Korea military defences during the exercises.
Tensions have been growing in the region after the North conducted its fourth nuclear test in January and threatened to annihilate its enemies.
The landing and assault drills on South Korea's east coast were part of eight weeks of joint exercises between the allies which the South has said are the largest ever.
Around 17,000 American troops and more than 300,000 South Koreans took part in the war exercises, which also involved 55 US aircraft and 30 South Korean ships.
The North has denounced the exercises as "nuclear war moves" and threatened to respond with an all-out offensive involving "an ultra-precision blitzkrieg strike of the Korean style".
The South Korean and U.S. militaries have said they had notified the North of "the non-provocative nature" of the exercises.