US and South Korean warships were today put on heightened alert after North Korea declared that it felt no longer bound to the truce that halted fighting in the Korean War.

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.

US spy satellites have detected signs that North Korea has restarted its nuclear plant, it was reported today.