North Korea said Wednesday it was abandoning the truce that ended the Korean war and warned it could launch a military attack on the South, two days after testing an atomic bomb for the second time.

The announcement came amid reports that the secretive North, which outraged the international community with its bomb test Monday, was restarting work to produce more weapons-grade plutonium.

Defying global condemnation, the regime of Kim Jong-Il said it could no longer guarantee the safety of US and South Korean ships off its west coast and that the Korean peninsula was veering back towards war.

The White House said it viewed Pyongyang's threats as "saber-rattling and bluster" that would only deepen its isolation, with spokesman Robert Gibbs saying that "threats won't get North Korea the attention it craves."

US Secretary of State Hillary Clinton meanwhile stressed US commitments to defend South Korea and Japan, saying in Washington "that is part of our alliance commitment that we take very seriously."