MOSCOW, May 27 (RIA Novosti) - North Korea, which sparked international alarm with a recent nuclear test, warned the South on Wednesday of an immediate military strike if attempts are made to intercept ships under a U.S.-led non-proliferation deal.

On Tuesday South Korea joined the Proliferation Security Initiative, aimed at preventing the transfer of banned weapons, in response to North Korea's nuclear test explosion. Participants in the initiative must ensure that their national facilities are not used for the transport of illegal weapons.

North Korea said in a statement carried by its official news agency: "As declared to the world, our revolutionary forces will consider the full participation in the Proliferation Security Initiative by the [South Korean President] Lee Myung-bak group of traitors as a declaration of war against us."

The military's statement, released by the Korean Central News Agency and translated by South Korea's Yonhap, said the country "will be no longer bound to the armistice agreement" that ended the 1950-53 war, and that the peninsula will be soon return to a state of war if the armistice is not adhered to.

North Korea fired two short-range missiles on Tuesday in apparent defiance against international pressure over its recent nuclear test. The UN Secretary General condemned the nuclear test blast, voicing concern that it could harm regional security and damage the non-proliferation regime.

The Proliferation Security Initiative was launched by the U.S. in 2003 after scud missiles were found on a North Korean cargo ship, but could not be seized under international law. The campaign includes searches of ships carrying suspicious freight.

Washington has welcomed South Korea's decision to join the campaign, saying it looks forward to working with Seoul to "advance the nonproliferation goals of the PSI."