There are new concerns tonight North Korea may be increasing its nuclear weapons arsenal.

The website "Beyond Parallel" released the pictures this week claiming to show work being done on a new nuclear submarine. 

Military analysts believe the sub could hold at least three ballistic missiles that could contain a nuclear warhead.

The concern is each missile could be launched underwater, which would be harder for the U.S.to track.

South Korea's Ambassador to the U.S. said he's confident the situation with North Korea can be resolved diplomatically.

"I am grateful President Trump and his staff has been working very hard to engage the North Koreans and try to resolve this problem," said Ambassador Cho Yoon-je. "Together with South Korea for the complete denuclearization of the Korean Peninsula."

The ambassador made his first trip to Anchorage Friday to take part in an annual ceremony that honors Korean War veterans in Alaska on behalf of the South Korean Government.

The U.S. says it has been aware of the new North Korean sub for the last year-and-a-half.

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