SEOUL, South Korea — A state-run newspaper in North Korea said Monday the communist country had carried out a threat to cancel the 1953 armistice that ended the Korean War, following days of increased tensions over its latest nuclear test.

A U.N. spokesman said later in the day, however, that North Korea cannot unilaterally dissolve the armistice.

North Korea also followed through on another promise: It shut down a Red Cross hot line that North and South Korea used for general communication and to discuss aid shipments and separated families’ reunions.

Enraged over the South’s current joint military drills with the United States and last week’s U.N. sanctions imposed on Pyongyang for its Feb. 12 nuclear test, North Korea has piled threat on top of threat, including a vow to launch a nuclear strike on the U.S.

Seoul has responded with tough talk of its own and has placed its troops on high alert. Tensions on the divided peninsula have reached their highest level since North Korea rained artillery shells on a South Korean island in 2010.

The North Korean government made no formal announcement on its repeated threats to scrap the 60-year-old armistice, but the country’s main newspaper, Rodong Sinmun, reported that the armistice was nullified Monday as Pyongyang had said it would.

The North has threatened to nullify the armistice several times before, and in 1996 it sent hundreds of armed troops into a border village. The troops later withdrew.

Despite the North Korean report, U.N. spokesman Martin Nesirky said the armistice is still valid and still in force because the armistice agreement had been adopted by the U.N. General Assembly and neither North Korea nor South Korea could dissolve it unilaterally.

“The terms of the armistice agreement do not allow either side unilaterally to free themselves from it,” said Nesirky, the spokesman for U.N. Secretary-General Ban Ki-moon.

Ban urged North Korea “to continue to respect the terms of the armistice agreement as it was approved by the General Assembly,” Nesirky said, adding that officials at U.N. headquarters in New York were unaware of any operational changes on the ground on the Korean peninsula.

White House spokesman Jay Carney said the U.S. was “certainly concerned by North Korea’s bellicose rhetoric. And the threats that they have been making follow a pattern designed to raise tension and intimidate others.”

He added that Pyongyang “will achieve nothing by threats or provocation.”