The mutual warnings also represented a clash of nerves between the young North Korean leader, who is building his credentials as head of his militaristic country, and Park Geun-hye, South Korea’s first female president, who has stressed security as her top priority.

While experts say North Korea does not have the technical ability to use nuclear-tipped missiles, that did not stop it from threatening to deploy them.

 

  “If we push the button, they will blast off and their barrage will turn Washington, the stronghold of American imperialists and the nest of evil, and its followers, into a sea of fire,” said Kang Pyo-yong, the vice defense minister of North Korea.

 

  His speech Thursday in the capital, Pyongyang, was carried Friday by the North’s main party newspaper, Rodong Sinmun. On Saturday, the Foreign Ministry issued a statement repeating that the North’s “status as a nuclear state” would become “permanent,” and calling its nuclear arsenal the strong guarantee of its sovereignty and security.

 

  In the last few days, North Korea’s state-run news media have carried a slew of official remarks threatening to launch “pre-emptive nuclear strikes” at the United States and South Korea with “lighter and smaller nukes,” hinting that the country has built nuclear warheads small enough to mount on long-range missiles. But American and South Korean officials strongly doubt that the North has mastered that technology, despite its launching of a long-range rocket in December and its nuclear test last month.

South Korean military officials called the remarks bluster, designed not so much to threaten Washington as to infuse the North with a sense of crisis and empowerment as Mr. Kim consolidates his grip on power and uses his country’s growing confrontation with the outside world to enhance his status at home.

The North’s state media has shown tearful soldiers running into his arms or shaking their rifles overhead in jubilation during Mr. Kim’s visits to their units. North Korean television reports have also shown soldiers rushing waist-deep into the ocean to see Mr. Kim off after a recent visit to a front-line island. Such scenes are not unusual in North Korea, where the state media depicts the nation’s leader as a fatherlike protector and calls for unconditional adoration and obedience.

 

  Ms. Park, however, warned that with its behavior, North Korea was only hurting itself.

North Korea “will collapse in self-destruction if it continues to waste its resources on nuclear weapon development while its people are going hungry,” she said Friday at a commission ceremony for young military officers.

 

  Also Friday, North Korea said it was nullifying all denuclearization agreements and cutting off the North-South hot line, in retaliation for the United Nations sanctions and the joint military exercises South Korea is staging with the United States.

 

  The North said this week that it considered the 1953 armistice agreement that halted the Korean War to be null and void as of Monday because of the joint military exercises. The North has threatened to terminate that agreement before, but American and South Korean military officials pointed out that legally, no party armistice can unilaterally terminate or alter its terms.

The Americans and South Koreans were not dismissing the threat entirely. Gen. James Thurman, the American commander in charge of enforcing the armistice conditions, said in a statement: “It is concerning when any signatory to a mutual agreement makes a public statement contrary to that agreement.”