North Korea government announced Wednesday that it regards the 1953 armistice of the Korean War as void, meaning it could no longer guarantee the safety of U.S. and South Korean vessels in the Yellow sea.

North Korea's latest threat came after Seoul announced that it was joining the U.S.-led Proliferation Security Initiative (PSL), launched under George W. Bush administration as part of its war on terror.

“If the armistice is terminated, the Korean peninsula, in legal terms, is bound to return to a state of war,” the North’s military said in a statement.

“Our country’s unstable situation, neither at war nor at peace, is coming to an extreme head. We do not know when war could break out.” the statement said.

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, a North Korean army spokesman was quoted as saying by the official KCNA news agency.

U.S. Secretary of State Hillary Clinton reaffirmed U.S. commitments to allies Japan and South Korea, said North Korea was behaving in a provocative and belligerent manner toward its neighbors, and that there were consequences to such behavior.

Russia also called the North Korean ambassador to the foreign ministry and told him Moscow has serious concern over this week's test, the ministry said.

Both Moscow and Washington said they hoped Pyongyang would return to the six-party talks aimed at ending its nuclear program.