: "The US military is neither confirming nor denying the reports, but the reports say it is an undeniable fact that the US is tracking our submarines and gathering information.
"There is no guarantee that should a clash arise between the strategic submarines of nuclear powers in the area, this will not escalate to a nuclear war.
"We are prepared to deal with any form of war the US wants.
"The US will have to take full responsibility for the resulting catastrophic consequences."
It comes just days after a North Korean defector claimed the police state is in the process of developing a 3,000-tonne nuclear sub.
Kim Heung-kwang said: “The decision for this development was made by Kim Jong-un and his advisors, who wanted to create an environment in which the US and international society can’t easily underestimate the North’s preemptive nuclear strike capability.”
Kim Jong-Un's nuclear-armed state believes US Navy ships have been entering its waters in a bid to keep tabs on regional rivals Russia and China.
The Chinese pledge to disregard a court ruling on claims in the South China Sea has led to strained relations between Washington and Beijing.
China has traditionally acted as a mediating influence between North Korea and the US.
But Pyongyang has been issuing increasingly-violent threats to the US, including one video which simulated the White House being destroyed by a nuclear explosion.
North Korean scientists have been gradually building up an atomic arsenal and carrying out a series of underground tests.
Last month, its military carried out a successful test launch of a missile - capable of carrying a nuke - from a submarine.
The ballistic missile travelled 300 miles before landing in Japanese waters.
We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368