North Korea, on Wednesday threatened to attack South Korea if it intercepted any of the communist nation’s ships as part of an anti-proliferation initiative, further raising tensions on the peninsula after a nuclear warhead test on Monday.

Pyongyang 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.