Is Russian tech behind North Korea's new nuclear submarine?

A major question is emerging over North Korea's unveiling of what it claims to be an 8,700-ton nuclear-powered strategic guided-missile submarine - whether Russia has assisted Pyongyang in securing the naval reactor technology that would make such a leap possible.

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The submarine under construction, revealed during North Korean leader Kim Jong Un's onsite inspection and reported by the North's state media, the Korean Central News Agency (KCNA), on Dec 25, is significantly larger than the US Navy's Virginia-class nuclear attack submarine.

KCNA said it represents an "epoch-making" upgrade in the North's nuclear war deterrent. Mr Kim reiterated that the development of the nuclear-armed fleet would serve as a "reliable shield" against perceived threats from the US-South Korea alliance.

With the rapid timeline and scale of progress Pyongyang claims, analysts in Seoul say suspicions of Russian assistance are difficult to dismiss.

"North Korea's nuclear submarine development had long seen little visible progress, but suddenly a nearly completed platform appears," said Mr Shin Jong-woo, a senior analyst at the Korea Defence and Security Forum in Seoul. "This strongly suggests the possibility of Russian support."

South Korea's military previously warned that strengthening Russia-North Korea military ties - driven by Pyongyang's supply of munitions and troops to Russia for its war in Ukraine - could expand into naval reactor technology transfers, a step that would have far-reaching implications for Northeast Asian security.