SEOUL — North Korea declared the 1953 Korean War armistice nullified on Monday, following through on a longstanding threat that it renewed last week amid rising tensions with South Korea and the United States.
A United Nations spokesman, Martin Nesirky, however, said the accord is still valid and in force, despite North Korea’s claim. He said the 60-year-old agreement ending the war had been adopted by the UN General Assembly and neither North Korea nor South Korea could dissolve it unilaterally.
Pyongyang’s announcement comes as the United States and South Korea are in the midst of two months of joint military drills, which started on March 1. On Monday they began another planned joint exercise that involved bringing 2,500 troops from the United States.
Stirring up a sense of crisis among its impoverished people, North Korea is also staging an unusually vigorous military drill of its own, South Korean officials said.
There were no signs, however, of hostility along the border between the two Koreas. South Korean officials said they were increasing their vigilance amid fears that North Korea might use the US-South Korean military drills and a fresh round of UN sanctions as an excuse to create an armed skirmish against the South.
“We must deal strongly with a North Korean provocation,’’ the South’s new president, Park Geun-hye, said during her first Cabinet meeting Monday. She called for the protection of people living on a border island that was attacked by North Korean artillery in 2010 and of South Koreans working in a joint industrial park in the North Korean border city of Gaesong. But she also said her two-week-old government would work to build ‘‘trust’’ with North Korea.
During the Cabinet meeting, Park also criticized senior military officers for playing golf last weekend amid the tensions with the North. Her office was investigating news reports that a military golf course in Seoul was crowded with senior army officers, including generals, on Saturday and Sunday.
The exchange of bellicose language between the two Koreas has recently intensified, recalling the level of tension after the North Korean artillery barrage in 2010, which killed four South Koreans.
After the United Nations imposed the new sanctions as a penalty for the North’s third nuclear test, on Feb. 12, the North said that it would nullify the armistice and that it was being threatened with a preemptive nuclear strike that it might itself preempt with nuclear strikes on Washington and Seoul.
South Korea responded that in the case of such attacks, the North Korean government would be ‘‘erased from the Earth.’’
On Monday, the North’s official Korean Central News Agency said that the armistice had been nullified. The North also cut off a Red Cross hot line the two Koreas used to discuss humanitarian issues.