Satellite photos of a North Korea shipyard suggest the country is building a submarine capable of launching nuclear missiles, experts say.

The images of Sinpo South Shipyard taken on Monday appear to show a new ballistic missile submarine, according to analysts at Washington-based think tank Beyond Parallel.

They appear to confirm reports that images in July showed North Korea’s leader Kim Jong-Un inspecting a submarine designed to carry nuclear weapons.

The new images, taken by Beyond Parallel, a project funded by the Centre for Strategic and International Studies (CSIS), show “support vessels and a crane” which suggest “possible preparations for a test”, analysts Joseph Bermudez and Victor Cha said in their report.

If a nuclear-capable submarine is built, it would be more difficult for the US and its allies to track, according to the analysts.

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“The construction and commissioning of a true SSB (ballistic missile submarine) capability would represent a significant advancement of the North Korean ballistic missile and nuclear threat and complicate defence planning in the region, given the difficulties of tracking and/or pre-emptively targeting such capabilities,” they said in their report.

According to the analysts, the latest “images suggest North Korea is making real progress in developing a second leg of the nuclear triad, bringing them closer to a survivable nuclear force.”

While North Korea media reports suggest the submarine’s deployment is “near at hand”, the experts said it was more accurate to describe the threat as “emerging, rather than imminent” since it could take more than a year to fit it out and put through trials.

A group of people can reportedly be seen in the images at the dock of the shipyard, where about 15 cranes have been installed in the past year, according to the report.

Satellite image showing an overview of Sinpo South Shipyard, in North Korea, on 26 August 2019. (Airbus/CSIS/Beyond Parallel)

Mr Bermudez and Mr Cha, however, admitted the images do not show a new ballistic missile submarine at the shipyard.

Recent short-range missile tests by North Korea’s capital city, Pyongyang, have triggered alarm in neighbouring Japan even as US president Donald Trump dismissed the launches as unimportant.

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The United Nations Security Council discussed North Korea’s actions behind closed doors on Tuesday at the request of Germany, France and Britain.