North Korea enters "state of war" against South
Pyongyang has also threatened to close a border industrial zone.
SEOUL - North Korea said on Saturday it was entering a "state of war" with South Korea, but Seoul and its ally the United States played down the statement as tough talk.
Pyongyang also threatened to close a border industrial zone, the last remaining example of inter-Korean cooperation which gives the impoverished North access to $2 billion (1.3 billion pounds) in trade a year.
The United States said it took Pyongyang's threats seriously but cautioned that the North had a history of bellicose rhetoric. Russia, another a permanent U.N. Security Council member, urged all sides to show restraint.
Tensions have been high since the North's new young leader Kim Jong-un ordered a third nuclear weapons test in February, breaching U.N. sanctions and ignoring warnings from North Korea's sole major ally, China, not to do so.
"From this time on, the North-South relations will be entering the state of war and all issues raised between the North and the South will be handled accordingly," a statement carried by the North's official KCNA news agency said.
KCNA said the statement was issued jointly by the North's government, ruling party and other organisations.
The Seoul government said there was nothing in the North's latest statement to cause particular alarm.
"North Korea's statement today ... is not a new threat but is the continuation of provocative threats," the South's Unification Ministry, which handles political ties with the North, said in a statement.
On Friday, Kim signed an order putting the North's missile units on standby to attack U.S. military bases in South Korea and the Pacific, after the United States flew two nuclear-capable stealth bombers over the Korean peninsula in a rare show of force.
U.S. officials described the flight as a diplomatic sortie aimed at reassuring allies South Korea and Japan, and at trying to nudge Pyongyang back to nuclear talks, though there was no guarantee Kim Jong-un would get the message as intended.
The two Koreas have been technically in a state of war since a truce that ended their 1950-53 conflict. Despite its threats, few people see any indication Pyongyang will risk a near-certain defeat by re-starting full-scale war.
There was no sign of unusual activity in the North's military to suggest an imminent aggression, a South Korean defence ministry official said.