North Korea boasted of being a "proud nuclear power" and threatened Monday to harm the U.S. if attacked as tensions mounted over a possible crackdown on exports of suspected missile parts from the North. President Barack Obama said the US is ready to cope with "any contingencies" involving North Korea and vowed not to "reward belligerence and provocation." South Korea's YTN news network reported Sunday that a US Navy destroyer tailing a North Korean ship suspected of carrying missiles and related parts was headed toward Myanmar in what could be the first test of new UN sanctions against the North over its recent nuclear test. The sanctions - punishment for an underground nuclear test North Korea conducted May 25 - firm up an earlier arms embargo against North Korea and authorize ship searches in an attempt to thwart the regime's nuclear and ballistic missile ambitions. On Monday, North Korea's main Rodong Sinmun newspaper called it "nonsense" to say the country is a threat to the US, and instead claimed Washington was the one threatening the North. The paper also warned in a commentary that the country is prepared to strike back if attacked. "As long as our country has become a proud nuclear power, the US should take a correct look at whom it is dealing with," the editorial said. "It would be a grave mistake for the US to think it can remain unhurt if it ignites the fuse of war on the Korean peninsula." The North Korean newspaper also denounced Obama's recent pledge to defend and protect South Korea - even vowing to keep Seoul "under the US nuclear umbrella" - as an attempt to attack North with atomic bombs. Obama made the pledge in a joint statement after a summit last week with the president of South Korea Lee Myung-bak. North Korea calls its nuclear program a deterrent against the US, which Pyongyang routinely accuses of plotting to topple the communist regime. The US, which has 28,500 troops in South Korea, has said it has no such intentions, and has no nuclear weapons on the Korean peninsula. Obama said the US is prepared for any North Korean provocation, including the regime's reported threat to test-launch a long-range missile toward Hawaii. Japanese media have reported that the North Koreans appear to be preparing for a long-range test planned sometime around July 4, the Independence Day holiday. Defense Secretary Robert Gates has ordered additional protections for Hawaii as a precaution. "This administration - and our military - is fully prepared for any contingencies," Obama said Friday during an interview with CBS News' "The Early Show" to be broadcast Monday. "I don't want to speculate on hypotheticals," Obama said. "But I want ... to give assurances to the American people that the t's are crossed and the i's are dotted in terms of what might happen." A North Korean cargo ship, the Kang Nam, is expected to travel to Myanmar via Singapore, YTN said, citing an unidentified intelligence source in South Korea. Myanmar's military government, which faces an arms embargo from the United States and the European Union, reportedly has bought weapons from the North in the past. Two US officials said Thursday that the US military had begun tracking the ship, which left a North Korean port on Wednesday. One official said it's not entirely clear what the Kang Nam was carrying but that it had been involved in weapons proliferation in the past. A senior US military official told The Associated Press on Friday that a Navy ship, the USS John S. McCain, is relatively close to the North Korean vessel but had no orders to intercept it under the Security Council resolution and had not requested that authority. The official spoke on condition of anonymity because of the sensitivity of the issue. The US ship, a guided missile destroyer, is named after the grandfather and father of former US presidential candidate Sen. John McCain. Both were admirals. According to McCain, the United States must board the Kang Nam even without permission from Pyongyang if hard evidence shows it is violating UN resolutions by carrying missiles or forbidden other cargo. "I think we should board it. It's going to contribute to the proliferation of weapons of mass destruction to rogue nations that pose a direct threat to the United States," he said on CBS' "Face the Nation."