North Korea threatens South korea

North Korea, facing international sanction for this week's nuclear test, threatened on Wednesday to attack the South after Seoul joined a U.S.led initiative to check vessels suspected of carrying equipment for weapons of mass destruction.The threat came after South Korean media reported Pyongyang had restarted a plant that makes weapons-grade plutonium.President Barack Obama is working to form a united response to Monday's nuclear test, widely denounced as a major threat to stability that violates U.N. resolutions and brings the reclusive North closer to having a reliable nuclear bomb.A North Korean army spokesman reiterated that the country was no longer bound by the armistice signed at the end of the 1950-53 Korean War because Washington had ignored its responsibility as a signatory by drawing Seoul into the anti-proliferation effort.Any hostile act against our peaceful vessels including search and seizure will be considered an unpardonable infringement on our sovereignty and we will immediately respond with a powerful military strike,the spokesman for the North's army was quoted as saying by the official KCNA news agency.South Korea announced on Tuesday it was joining the naval exercise, called the Proliferation Security Initiative.An angry Pyongyang, which relies on arms sales for cash, had said it considered such a move an act of war.The nuclear test has raised concern about Pyongyang spreading weapons to other countries or groups. Washington has accused it of trying try to sell nuclear know-how to Syria and others.The rival Koreas have fought two deadly naval clashes in 1999 and 2002 near a disputed maritime border off their west coast and the North has threatened in the past year to strike South Korean vessels in those Yellow Sea waters.Pyongyang also test-fired a third short-range missile late on Tuesday after it added to tensions with the launch of two others earlier in the day, the South's Yonhap news agency quoted a unnamed government source as saying.The secretive state appears to have made good on a threat issued in April of restarting a facility at its Yongbyon nuclear plant that extracts plutonium, South Korea's largest newspaper, Chosun Ilbo, reported.The nuclear test was a grand undertaking to protect the supreme interests of the DPRK (North Korea) and defend the dignity and sovereignty of the country and nation, it quoted a communist party official as saying.North Korea's meager supply of fissile material is likely down to enough for five to seven bombs after Monday's test, experts have said. It could probably extract enough plutonium from spent rods at the plant for another bomb's worth of plutonium by the end of this year.The North's next step may to be resume operations at all of Yongbyon, with experts saying it could take the North up to a year to reverse disablement steps. Once running, it can produce enough plutonium for a bomb a year.