The North Korean submarine that was reportedly gone missing is now presumed to be sunk at sea.

The unknown class of vessel was operating off the North Korean coast when it disappeared, according to reports from the US and South Korea.

According to CNN, the US military had been observing the submarine off the North’s eastern coast, citing three US officials.

Kim Jong Un surveys a North Korean submarine.
Kim Jong Un surveys a North Korean submarine.

The incident comes amid the US and South Korea’s largest-ever military exercise, heightening tensions in the region. Around 17,000 U.S. military personnel and 300,000 South Korean troops are taking part of what they called the “largest ever” joint military exercises.

According to an unidentified US government source, The speculation is that it sank.”

The North Koreans have not made an attempt to indicate there is something wrong or that they require help or some type of assistance.”

North Korea’s Navy fleet operates around 70 submarines, most of them are aging diesel submarines.

But this old submarines still poses a threat to South Korean vessels.

In 2010, a Pohang-class corvette was reportedly torpedoed by a North Korean submarine near their sea border.

And in August last year, South Korea reported that around 50 North Korean submarines had left their bases and vanished from radar sparking fears they were readying for war.

The defence ministry in Seoul later that year said it had noted the ‘re-appearance’ of a large part of the submarine fleet, suggesting that some were still missing four days after they disappeared.