North Korean state media warned on Tuesday of a nuclear attack on the United States at any sign of American aggression as a U.S. Navy strike group steamed toward the western Pacific.
U.S. President Donald Trump, who has urged China to do more to rein in its impoverished neighbour, said in a tweet that North Korea was "looking for trouble" and the United States would "solve the problem" with or without China's help.
Tension has escalated sharply on the Korean peninsula amid concerns that reclusive North Korea may soon conduct a sixth nuclear test and after Washington said at the weekend it was diverting U.S. Navy strike group Carl Vinson from port calls to Australia toward the Korean peninsula as a show of force.
U.S. officials have stressed that stronger sanctions are the most likely U.S. course to press North Korea to abandon its nuclear program but Washington has said all options, including military ones, are on the table and that a U.S. strike last week against Syria should serve as a warning to Pyongyang.
North Korea's official Rodong Sinmun newspaper said the country was prepared to respond to any U.S. aggression.
"Our revolutionary strong army is keenly watching every move by enemy elements with our nuclear sight focused on the U.S. invasionary bases not only in South Korea and the Pacific operation theatre but also in the U.S. mainland," it said.
South Korea's acting President Hwang Kyo-ahn warned of "greater provocations" by North Korea and ordered the military to intensify monitoring and ensure close communication with Washington.
"It is possible the North may wage greater provocations such as a nuclear test timed with various anniversaries including the Supreme People's Assembly," said Hwang, acting leader since former president Park Geun-hye was removed amid a graft scandal.
Trump said in a tweet that a trade deal between China and the United States would be "far better for them if they solved the North Korea problem. If China decides to help, that would be great," he said. "If not, we will solve the problem without them!"
Trump and his Chinese counterpart Xi Jinping met in Florida last week and Trump pressed Xi to do more to rein in North Korea.
China's ambassador to the United Nations, Liu Jieyi, repeated China's call for a return to dialogue with North Korea. “The situation is tense and we certainly want a peaceful solution and we believe that it is highly important to move toward denuclearization, to maintain peace and stability and it’s time that different sides sit down to talk about achieving these objectives,” he told Reuters.
Asked about Trump linking a trade deal to China’s help with North Korea: “We need to look at the situation on the Korean Peninsula as something that we should work together on.”
North Korea convened a Supreme People's Assembly session on Tuesday, one of its twice-yearly sessions attended by leader Kim Jong Un, and reported a successful national budget execution and personnel appointments, the official KCNA news agency said. The agency made no mention of North Korea's nuclear weapons programme or being under threat from the United States.
South Korean officials sought to quell talk in social media of an impending security crisis.
"We'd like to ask for precaution so as not to get blinded by exaggerated assessment about the security situation on the Korean peninsula," Defence Ministry spokesman Moon Sang-kyun said.
Saturday is the 105th anniversary of the birth of Kim Il Sung, North Korea's founding father and grandfather of the current ruler. A military parade is expected in Pyongyang to mark the day. North Korea often also marks important anniversaries with tests of its nuclear or missile capabilities in breach of U.N. Security Council resolutions.
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