North Korea on Wednesday threatened military strikes after South Korea joined the U.S.-led Proliferation Security Initiative. The People's Army Commission in the truce village of Panmunjom in a statement threatened to "counter any hostile action against [North Korea], including checkup and inspection of its peaceful vessels, with prompt and strong military strikes."

North Korea's Committee for the Peaceful Reunification of the Fatherland also said Wednesday, "Provocations will be countered by practical actions corresponding to real war." Seoul on Tuesday finally made up its mind to join the PSI, whose members can stop and search ships suspected of carrying materials related to weapons of mass destruction. North Korea believes it is the chief target of the initiative.

The North's permanent military commission in Panmunjom said "Given that the U.S. has drawn the puppets" -- an epithet for South Korea – "into the PSI in defiance of its responsibility as a party to the armistice agreement, our military will no longer be bound by the armistice agreement." It said it could "no longer guarantee the legal status of the five South Korean islands located in waters south of our military sea boarder and the safety of South Korean and U.S. military ships and civilian vessels sailing along the western sea border."

North Koreans rally to celebrate at the Pyongyang Stadium on Tuesday what the North says was a successful second nuclear test, in this picture released by North Korea's official KCNA news agency early Wednesday. The sign at left reads: "Hurray for the great victory of the military-first politics!", and the the red propaganda sign reads, "Let's arm ourselves more thoroughly with revolutionary ideology of the great leader Kim Il-sung comrade!" /Reuters-KCNA

A government official here said the announcement was "a threat of retaliatory attacks" along the Northern Limit Line, the de facto maritime border off the west coast. In July 2003, when the PSI was first launched, North Korea said the U.S. reneged on Item 15 of the armistice agreement banning any blockade of North Korea and threatened "merciless retaliatory steps."

Seoul claims the PSI, which has 95 countries as members, is not targeted at any particular country. Prof. Nam Joo-hong of Kyonggi University said, "For the North to assert a violation of the armistice agreement mentioning 'marine blockade' when routine navigation of commercial vessels are not subject to the initiative is absurd." A diplomat said the navigation rights of private North Korean vessels will be guaranteed as usual under a 2005 inter-Korean maritime accord.

The question is how serious North Korea is. Since it conducted a nuclear test as threatened last month, it is quite possible that it will make good on the threat of military action.

"The North won't find it easy to launch a provocation causing huge damage right away," a government official said. "The chances are that Pyongyang will attempt to neutralize the NLL by firing a warning missile or artillery at South Korean vessels navigating nearby."