N. Korea threatens South, restarts plutonium plant

North Korea, facing international censure for this week's nuclear test, threatened yesterday to attack the South after it joined a US-led plan to check vessels suspected of carrying equipment for weapons of mass destruction.

Adding to tension in the region, South Korean media reported that Pyongyang had restarted a plant that makes plutonium that can be used in nuclear bombs.

In Moscow, news agencies quoted an official as saying that Russia is taking precautionary security measures because it fears mounting tensions over the test could escalate to war.

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.

US Secretary of State Hillary Clinton reaffirmed US commitments to allies Japan and South Korea, said North Korea was behaving in a "provocative and belligerent manner" toward its neighbours, and that there were consequences to such behaviour.

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

North Korea's latest threat came after Seoul announced, following the North's nuclear test on Monday, it was joining the US-led Proliferation Security Initiative, launched under the George W. Bush administration as a part of its "war on terror."

"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.

He reiterated that the North was no longer bound by an 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.

The UN Security Council is discussing ways to punish Pyongyang for Monday's test, widely denounced as a major threat to regional stability and which brings the reclusive North closer to having a reliable nuclear bomb.

Interfax news agency quoted an unnamed security source as saying a stand-off triggered by Pyongyang's nuclear test on Monday could affect the security of Russia's far eastern regions, which border North Korea.

"We are not talking about stepping up military efforts but rather about measures in case a military conflict, perhaps with the use of nuclear weapons, flares up on the Korean Peninsula," the source said.

Russian President Dmitry Medvedev told South Korean President Lee Myung-bak, who called him yesterday, that Russia would work with Seoul on a new UN Security Council resolution and to revive international talks on the North Korean nuclear issue.

The nuclear test has raised concern about Pyongyang spreading weapons to other countries or groups. Washington has accused it of trying to sell nuclear know-how to Syria and others.