North Korea delivered a fresh round of rhetoric on Thursday with claims it had "powerful striking means" on standby for a launch, while Seoul and Washington speculated that the country is preparing to test a medium-range missile during upcoming national celebrations.
On the streets of Pyongyang, meanwhile, North Koreans celebrated the anniversary of leader Kim Jong Un's appointment to the country's top party post - one in a slew of titles collected a year ago in the months after father Kim Jong Il's death.
The Committee for the Peaceful Reunification of the Fatherland, a non-military agency that deals with relations with South Korea, didn't elaborate on its warning of a strike.
The statement is the latest in a torrent of warlike threats seen outside Pyongyang as an effort to raise fears and pressure Seoul and Washington into changing their North Korea policy.
Officials in Seoul and Washington say Pyongyang appears to be preparing to test-fire a medium-range missile designed to reach the US territory of Guam in the Pacific Ocean.
Such a launch would violate UN Security Council resolutions prohibiting North Korea from nuclear and ballistic missile activity, and mark a major escalation in Pyongyang's standoff with neighbouring nations and the US.
North Korea already has been punished in recent months for launching a long-range rocket in December and conducting an underground nuclear test in February.
Analysts do not believe North Korea will stage an attack similar to the one that started the Korean War in 1950. But there are concerns that the animosity could spark a skirmish that could escalate into a serious conflict.
"North Korea has been, with its bellicose rhetoric, with its actions... skating very close to a dangerous line," US Defense Secretary Chuck Hagel said in Washington on Wednesday.
The missile that officials believe Pyongyang is readying has been dubbed the "Musudan" by foreign experts after the northeastern village where North Korea has a launch pad. The missile has a range of 3500 kilometers (2,180 miles) and is designed to reach US military installments in Guam and Japan, experts say.
Bracing for a launch, officials said could take place at any time, Seoul deployed three naval destroyers, an early warning surveillance aircraft and a land-based radar system, a Defense Ministry official said in Seoul, speaking on condition of anonymity in line with department rules. Japan deployed PAC-3 missile interceptors around Tokyo.
But officials in Seoul played down security fears, noting that no foreign government has evacuated its citizens from either Korean capital.
"North Korea has continuously issued provocative threats and made efforts to raise tension on the Korean peninsula... but the current situation is being managed safely and our and foreign governments have been calmly responding," Foreign Ministry spokesman Cho Tai-young told reporters on Thursday.