North Korea has lost a submarine during an exercise off the country’s east coast.
The North Korean navy has been hunting for the missing vessel for days, watched by US satellites, aircraft and ships, CNN reports.
US military officials believe the submarine, which they had been observing in operation, has suffered a failure. They are not certain if it has sunk, or simply lost contact with its base.
The loss of the submarine comes as the US and South Korea stage eight weeks of joint military exercises on the Korean peninsula, following North Korean nuclear tests and long-range missile launches earlier this year.
The joint training includes a simulated storming of North Korean beach defences. The operation involves 17,000 American troops, 300,000 South Koreans, 55 US marine aircraft and 30 ships.
The US and South Korean militaries said that "the non-provocative nature” of the exercises had been communicated to North Korea.
But North Korea said it would counter US and South Korean forces "with an ultra-precision blitzkrieg strike of the Korean style", Reuters reports.
Its leader Kim Jong-Un has reportedly ordered more nuclear capability trials, despite United Nations Security Council sanctions following the country’s fourth nuclear tests in January.
North Korea reportedly tested a submarine-launched ballistic missile in December, but Western experts are doubtful after footage released surrounding the tests appears to be fake.
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