NORTH KOREA said today 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.
The White House said today that it takes North Korea's latest sabre-rattling threats seriously while cautioning that Pyongyang has a long history of bellicose rhetoric.
The statement from Washington came as South Korea said there had been no unusual activity within the North's military since an angry statement from Pyongyang last night that it is entering "a state of war" with its neighbour.
The belligerent declaration came a day after North Korean leader Kim Jong-un signed off on an order putting its missile units on standby to attack US military bases in the South.
"We've seen reports of a new and unconstructive statement from North Korea. We take these threats seriously and remain in close contact with our South Korean allies," said Caitlin Hayden, spokeswoman for the White House National Security Council.
"But, we would also note that North Korea has a long history of bellicose rhetoric and threats and today's announcement follows that familiar pattern," she said.
This morning South Korea said there was no sign of any military activity to suggest the threat was anything other than more empty propaganda.
A South Korean Defence ministry official noted that no shots had been fired, no missiles readied, and that there was no unusual activity in the North's army.
The Kaesong industrial zone inside North Korea, run by companies from South Korea, was open for business and hundreds of South Korean workers crossed the border as usual on Saturday.
Hours later, however, Pyongyang threatened to shut down the jointly run zone, expressing anger over media reports suggesting the complex remained open because it was a source of hard currency for the impoverished North.
"If the puppet group seeks to tarnish the image of the DPRK even a bit, while speaking of the zone whose operation has been barely maintained, we will shut down the zone without mercy," an identified spokesman for the North's office controlling Kaesong said in comments carried by KCNA.
South Korea's Unification Ministry responded by calling the North Korean threat "unhelpful" to the countries' already frayed relations and vowed to ensure the safety of hundreds of South Korean managers who cross the border to their jobs in Kaesong. It did not elaborate.
The Associated Press, the only foreign media organisation to have a bureau in North Korea, reported on Saturday that "inside Pyongyang, much of the military rhetoric feels like theatrics".
It noted that while 100,000 people were summoned to Kim Il Sung square on Friday for a mass rally, "it was business as usual at restaurants and shops, and farms and factories, where the workers have heard it all before".
BR Myers, a North Korea expert at Dongseo university in Busan, told the New York Times: "I have to say from watching North Korea's evening news broadcasts for the past week or so, the North Korean media are not quite as wrapped up in this war mood as one might think. The announcers spend the first 10 minutes or so reporting on peaceful matters before they start ranting about the enemy."
There was also little sign of panic on the streets of Seoul, where a population accustomed to North Korean bombast continued its daily business.
The US in recent weeks has mounted its own displays of military might in response to the increasingly belligerent rhetoric out of Pyongyang.
Two nuclear-capable B2 stealth bombers flew an unusually public training mission alongside South Korean forces on Thursday, where they simulated dropping munitions on an island near the Koreas' shared border. In a reminder of the reach of America's military, the aircraft flew for 37 straight hours during the round-trip flight from Missouri.
Earlier this month, the US announced it was bolstering its stock of missile interceptors along the Pacific coast in response to the growing threat from North Korea.
Chuck Hagel, the US secretary of defense, said the North had shown "advances in its capabilities" and the US would respond by deploying an additional 14 missiles to Alaska, the state most at risk from a possible strike.
The reinforcements will mean a total of 44 interceptors in place by the end of 2017, enough to bring down 22 incoming missiles. While North Korea is thought to be far from that level of stockpile, Mr Hagel said the US was determined to stay "ahead of the threat".
"We remain fully prepared and capable of defending and protecting the United States and our allies," said Ms Hayden. "We continue to take additional measures against the North Korean threat, including our plan to increase the US ground-based interceptors and early warning and tracking radar," and the recent signing of a South Korean-US counter-provocation plan.
The two Koreas have been in a state of war for six decades, with no formal end to the 1950 Korean war. An armistice was put in place in 1953.
American officials told the New York Times that the US is relaxed about North Korea's threats of war, but concerned that Kim Jong-un's unpredictable behaviour could lead to more cyber-attacks or other small-scale acts of aggression.
"We are convinced this is about Kim solidifying his place with his own people and his own military, who still do not know him," one unnamed senior administration official told the newspaper on Friday.
He added: "We are worried about what he's going to do next, but we are not worried about what he seems to be threatening to do next."