Japanese, South Korean and US missile-destroying ships set sail to monitor North Korea's imminent rocket launch, as Pyongyang stoked tensions Monday by detaining a South Korean worker for allegedly denouncing the North's political system. North Korea says it will send up a communications satellite into orbit sometime between April 4 and 8. The US, South Korea and Japan suspect the regime is using the launch to test its long-range missile technology, warning it would face UN sanctions under a Security Council resolution banning the country from any ballistic activity. North Korea has threatened to quit international disarmament talks on its nuclear programs if punished with sanctions. The country's main Rodong Sinmun newspaper reiterated that warning Sunday, saying the talks will "completely collapse" if taken to the Security Council. Further heightening tensions on the divided peninsula, North Korean authorities detained a South Korean worker at a joint industrial zone in the North for allegedly denouncing Pyongyang's political system and inciting female northern workers to flee the communist country. North Korea assured Seoul it would guarantee the man's safety during an investigation, according to the South Korean Unification Ministry, which handles relations with the North. The detention comes as two American journalists working for former Vice President Al Gore's Current TV media venture remain in North Korean custody after allegedly crossing the border illegally from China on March 17. Late Monday, the North also threatened to take an unspecified "resolute countermeasure" against South Korea if it joins a US-led international campaign aimed at stopping the spread of weapons of mass destruction. South Korea has only been an observer to the Proliferation Security Initiative, but Seoul officials recently said they were considering fully joining the program after the North's rocket launch. Seoul's participation would be treated as "a declaration of a war," Pyongyang's Committee for the Peaceful Reunification of Korea said in a statement carried by the official Korean Central News Agency. In preparation for the rocket launch, Japan deployed Patriot missiles around Tokyo and sent warships armed with interceptors to the waters between Japan and the Korean peninsula as a precaution, defense officials said. Two US destroyers anchored at a South Korean port after holding military exercises with the South Korean navy also are believed to have departed for waters near North Korea to monitor the rocket launch. The USS McCain and the USS Chafee left Busan on Monday, a US military spokesman said. He declined to disclose their destination and spoke on condition of anonymity, saying he was not authorized to discuss the ships' routes. South Korea also is dispatching its Aegis-equipped destroyer, according to a Seoul military official who asked not to be named, citing department policy. All of the warships - of South Korea, Japan and the US - are equipped with sophisticated combat systems enabling them to track and shoot down enemy missiles. However, leaders of all three countries have indicated it's unlikely the warships will respond militarily to the North's launch. South Korean President Lee Myung-bak said in an interview with the Financial Times published Monday that his government opposes any military response to the North's launch, saying that would be unhelpful in talks on dismantling North Korea's nuclear program. In Washington, US Defense Secretary Robert Gates said in a TV interview aired Sunday that the US has no plans to intercept the North Korean rocket but might consider it if an "aberrant missile" were headed to Hawaii "or something like that." Japan had earlier hinted that it might shoot down the rocket, but now says it will only fire interceptors if debris from a failed launch appears likely to hit Japanese territory.