South Korea has accused the reclusive North of torpedoing one of its warships, heightening tension in the region and testing the international position of China, Pyongyang's only major backer.
South Korea said it would take "firm" measures against its impoverished neighbour, which responded furiously by saying that it was ready for war if Seoul or its allies imposed sanctions.
A report by investigators, including experts from the United States, Australia, Britain and Sweden, concluded that a North Korean submarine had fired the torpedo which sank the Cheonan corvette in March, killing 46 sailors.
International condemnation came immediately after the accusation, with the stark exception of China, which analysts say is desperate to avoid any action that might destablise its reclusive neighbour and lead to a spill-out into its territory.
A senior South Korean government official said previously that the attack appeared to have been in revenge for a firefight near the disputed North-South border late last year in which the North's navy was humiliated.
UN Secretary-General Ban Ki-moon called the contents of the South Korean investigation deeply troubling.