The latest threat, reported by the official Korean Central News Agency, comes as South Korea, Japan and the United States remained on the alert for any imminent ballistic missile test by the North, which, military experts have said, could come any time. Monday passed without any missile test as North Korean leader Kim Jong Un and his regime observed the 101st birthday of his late grandfather and founder of the country, Kim Il Sung.
In Seoul, the occasion was market by an anti-North Korean rally. A portrait of the late Kim Jong Il, father of the current leader, was reportedly burned.
Taking serious note of the rally, the North's "supreme command of the Korean People's Army Tuesday issued an ultimatum to the South Korean puppet group," reported KCNA, carried by Yonhap News.
Separately, CNN, citing the KCNA, reported the North considered the rally a "monstrous criminal act" and that its "retaliatory action will start without any notice from now."
North Korea also said the South must first apologize for all its past anti-North Korean acts if it wants an inter-Korean dialogue.
South Korean President Park Geun-hye and her Unification Minister Ryoo Kihl-jae last week had proposed a dialogue with the North. However, the North, irate over tightened U.N. Security Council sanctions for its third nuclear test in February and its missile tests, has maintained its barrage of dangerous threats including pre-emptive nuclear strikes against the United States and South Korea, raising tensions on the Korean Peninsula that have forced its neighbors to stay on high alert.
A representative of the North's Committee for the Peaceful Reunification of Korea had earlier termed Park's dialogue proposal insincere and an insult.
Separately, Xinhua, the official news agency of China, a close ally of the North, quoted South Korean Defense Ministry spokesman Kim Min-seok as telling reporters Monday the time for a missile launch likely could be lengthened.
The government and the military "have continued to say that North Korea can launch missiles after April 10," Kim was quoted as saying. "But, five days have already passed since then, and (the launch period) can be lengthened under such circumstances."
Kim said the North injected fuel into the missiles before April 10 and it can fire them at any moment when a political decision is made, Xinhua said.
The report said the North is believed to have moved its Musudan intermediate-range missiles to its east coast. Other missiles, including Scud and Nodong, were also believed to be mounted on mobile launchers known as the transporter-erector launchers, it said. The Musudan is estimated to have a range of about 3,500 kilometers and reach the U.S. military base in Guam, Xinhua said.