North Korea says it is scrapping all non-aggression pacts with South Korea, closing its hotline with Seoul and shutting their shared border point.
The announcement follows a fresh round of UN sanctions punishing Pyongyang for its nuclear test last month.
Earlier, Pyongyang said it reserved the right to a pre-emptive nuclear strike against its “aggressors”.
The US said it took the threats seriously, but that “extreme rhetoric” was not unusual for Pyongyang.
South Korea’s defence ministry said that the North would become “extinct” if it went through with its threat.
The North Korean announcement, carried on the KCNA state news agency, said the North was cancelling all non-aggression pacts with the South and closing the main Panmunjom border crossing inside the Demilitarized Zone.
FLASHBACK 27 May 2009: North Korea abandons truce and threatens to attack the South
Pyongyang said that South Korea’s decision to start intercepting ships that are suspected of carrying weapons of mass destruction was tantamount to “a declaration of war against us”.
The statement follows a number of missile tests and an underground nuclear test by the North in the last two days.
The statement, through North Korea’s state newswire, warned Seoul that North Korea “will no longer be bound by the armistice accord” and that the “Korean peninsula will go back to a state of war”.
Pyongyang had previously warned Seoul that joining the US-led Proliferation Security Initiative (PSI) would have fearful consequences.
No formal peace treaty has ever been signed between the two countries, but an armistice in 1953 and a Mutual Defence treaty between the US and South Korea effectively ended the Korean war.
