NEW satellite images of North Korea bases appear to show the volatile state is overhauling its missile sub fleet as tension rises during the nuclear stand-off between Kim Jong-un and the US.

The pictures show activity at a test site which is scarily similar to preparations before the Stalinist nation's last test of their Pukguksong-1 submarine-launched ballistic missile in August 2016.

7 The North Korean subs were seen in commercial satellite pictures Credit: Getty - Contributor

7

7 North Korea released this image showing its submarine-launched missile Credit: AFP - Getty

The images emerged after Trump warned North Korea that the US military was "locked and loaded" as Pyongyang accused the U.S. leader of driving the Korean peninsula to the brink of nuclear war.

The Pentagon said the United States and South Korea would proceed as planned with a joint military exercise in 10 days, an action sure to further antagonise North Korea.

North Korean watcher Joseph Bermudez of 38North, which monitors military activity in the Stalinist country, has spotted changes on the boat and the facility it is docked in.

He said: "Recent commercial satellite imagery reveals several developments suggesting that North Korea may be accelerating the development of the sea-based leg of its nuclear forces.

"Since the July report, netting or tarps have been suspended above both the fore and aft decks of the submarine obscuring any activity taking place beneath them.

"The only other time this was seen was during May-July 2016 and prior to the failed July 9, 2016 Pukguksong-1 test."

7 North Korea appears to be attempting to upgrade its fleet of subs Credit: Getty - Contributor

7 The pictures emerge as tension between the US and North Korea grows Credit: Getty - Contributor

7 The facilities and buildings appear to have been upgraded Credit: Getty - Contributor

7 Kim Jong-un has been repeatedly threatening to nuke America and it's feared his next launches will be seaborne Credit: Reuters

Long-range ballistic missiles (ISBMs), and their submarine-housed counterparts (SLBMs), are rockets which can carry nuclear bombs and would be capable of striking the west coast of the US including cities such as Los Angeles and Seattle.

However, North Korea is not believed to have developed the technical capacity to mount a nuclear warhead on an SLBM.

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Officials told CNN that North Korea is developing its submarine based missile capability.

Researchers believe the threat posed by Kim Jong-un has been underestimated – with the latest missile test soaring seven times higher than the International Space Station.

North Korea announced the completion of its first ever successful intercontinental ballistic missile launch last month.

The ICBM was the first of its kind to be launched by the secret state and the test sent shockwaves across the world after the trigger-happy tyrant vowed to turn the US into a “pile of ash”.

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A successful ICBM test launch marks a significant step forward for secretive Pyongyang's weapons capability.

ICBMs have a minimum range of about 3,418 miles, but some are designed to travel 6,214 miles or further.

California is roughly 5,592 miles from North Korea.

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