(Bloomberg) -- Satellite imagery indicates North Korea has started construction of a new submarine, a report from a research group said, as Kim Jong Un has called for enhancing his ability to launch nuclear attacks from under the sea.

Hull components and equipment used in submarine construction have been seen at the Sinpho South Shipyard, the US-based 38 North website reported Wednesday. The submarine under construction could likely be of similar size to the latest vessel built at the facility, which was a tactical attack submarine that North Korea claimed could fire missiles with nuclear warheads.

Over the past few months, satellite imagery shows submarine components of similar dimensions to the last North Korean submarine as well as construction equipment used in building the boats have been brought to the shipyard, according to the website, which is a publication of the Stimson Center think tank. 

Kim has placed a high priority on building missile-capable submarines. His current fleet of submarines makes enough noise underwater that the vessels are unable to stray far from the coast without being tracked. But they add to contingencies the US and its allies much take into account as they prepare counter-measures for a possible North Korean strike.

Read more: North Korea Displays New ‘Tactical Nuclear Attack’ Submarine

In September, North Korea had a launching ceremony for its new attack sub named the Hero Kim Kun Ok. The initial images showed the submarine, which would be its second built to shoot off ballistic missiles, likely has 10 tubes and is a modernized Soviet-designed Romeo Class boat, specialist publication Naval News said in an analysis.

North Korea’s current submarines are all conventionally powered, but Kim may be seeking technology from Russia that would help in building a nuclear-powered submarine, the New York Times reported last year before the North Korean leader crossed the border to have a summit with President Vladimir Putin. 

South Korea’s military has expressed doubts about the capability of the two North Korean submarines built to fire missiles and satellite photos have indicated one of the boats returned to the shipyard for repairs after firing off a rocket in a test launch. 

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