North Korea threatened yesterday to attack the South if Seoul intercepted any of Pyongyang's ships to check for weapons shipments - further raising tensions on the peninsula after a nuclear warhead test on Monday.

The communist North also said it regarded the 1953 armistice of the Korean war as void, meaning it could no longer guarantee the safety of US and South Korean vessels in the Yellow Sea, scene of battles in 1999 and 2002, with dozens of casualties.