North Korea’s military is clandestinely building a nuclear-powered submarine, according to a Japanese newspaper report, the latest provocation by Pyongyang in an escalating clash with the U.S. and its allies in a region already on edge.

The report by Japan’s Sekai Nippo, citing an “informed” but unidentified “source familiar with the North Korean situation,” said the size of the nuclear-powered submarine under construction is unclear but that the Kim Jong-un regime in Pyongyang hopes to have it deployed within three years.

The claim could not be independently verified by The Washington Times, and U.S. intelligence sources could not immediately be reached for comment. If true, however, the claim could indicate a dramatic step forward for North Korea’s navy, which analysts estimate operates a fleet of 50 to 60 diesel-electric submarines that are louder and easier to detect than the nuclear-powered vessels.

North Korea is expected to be a prime focus of President Trump’s week in New York meeting with other world leaders at the U.N. General Assembly. On Twitter, Mr. Trump revealed that he had spoken with South Korean President Moon Jae-in Sunday about Pyongyang. His tweet mocked Mr. Kim as “Rocket Man” and boasted about the effectiveness of international sanctions to cut off the North’s energy supplies.

“President Trump and President Moon committed to continuing to take steps to strengthen deterrence and defense capabilities, and to maximize economic and diplomatic pressure on North Korea,” the White House said in a statement. Mr. Kim, who rarely travels, will not be in New York, but North Korean Foreign Minister Ri Yong-ho is expected to address the world body Friday. Continue reading.