North Korea could be ramping up its submarine-launched ballistic missile program (SLBM) as latest satellite images show the presence of a second submersible test-stand barge.

According to 38 North, a Korean watchdog site hosted by Johns Hopkins University's US-Korea Institute, the alleged barge was detected on Pyongyang's west coast in aerial photos taken from the Nampo Naval Shipyard.

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"The discovery of a second missile test barge may have a number of implications for the future of North Korea's SLBM program that appears to be an important priority for Kim Jong-un," the analysis wrote.

"Barges such as these are used by navies to conduct underwater tests of new and modified submarine missile launch tubes and launch systems, as well as to conduct initial missile test launches before these systems are installed in a submarine," the report, written by Joseph S. Bermudez Jr., said.

It is not clear if the Pyongyang made or bought the barge from another country.

North Korea has conducted at least six KN-11 (Pukguksong-1) missile test launch from its other barge at the Sinpo South Shipyard, Sputnik News reported.

Meanwhile, North Korea has also expanded its nuclear arsenal to 30 warheads and is expected to increase further as it produces more weapons-grade plutonium and uranium, according to the Institue of Science and International Security in Washington said.

The country will control enough fissile material to increase the arsenal number twofold to as many as 60 weapons by the end of the decade. The rapid increase, however, is a cause for concern as the US previously estimated in 1999 that North Korea will only own around one or two nuclear weapons and would only increase it up to 10 or more by 2020.

That being said, Pyongyang is starting to emerge as a world nuclear power and has the capability to initiate a strike on neighboring regions. But David Albright, the institute's founder and director, noted that even though North Korea could "theoretically use a satellite launcher" to attack the US, it is "not with any reliability."