North Korea issued new threats against South Korea on Tuesday, vowing "sledge-hammer blows" of retaliation if South Korea did not apologize for anti-North Korean protests the previous day when the North was celebrating the birth of its founding leader.
On Monday, the North dropped its shrill threats of war against the United States and South Korea as it celebrated the 101st anniversary of the birth of its first leader, Kim Il-Sung, raising hopes for an easing of tension in a region that has for weeks seemed on the verge of conflict.
The hint of a scaling back of the confrontation followed offers of talks with the isolated North from both the United States and the South.
But the North's KCNA news agency said on Tuesday the North Korean army had issued an ultimatum to the South after rallies in the South on Monday at which portraits of North Korea's leaders were burned.
"Our retaliatory action will start without any notice from now," KCNA reported, citing military leaders of the Democratic People's Republic of Korea (DPRK), as North Korea is officially known.
"The military demonstration of the DPRK's revolutionary armed forces will be powerful sledge-hammer blows at all hostile forces hurting the dignity of the supreme leadership."
South Korean media reported several small demonstrations in the capital, Seoul, on Monday. One television station showed pictures of a handful of protesters burning a portrait of North Korean leader Kim Jong-un.
Small counter-protests, by South Koreans calling for dialogue with the North, were also held, media reported.
The North has threatened nuclear attacks on the United States, South Korea and Japan after new U.N. sanctions were imposed in response to its latest nuclear arms test in February.
The North has also been angry about annual military exercises between U.S. and South Korean forces, describing them as a "hostile" act. The United States dispatched B52 and B2 stealth bombers from their bases to take part.
Offer of Talks
But on Tuesday, the North's KCNA did not threaten the United States, reserving its anger for what it calls South Korea's "puppet" government.
It even mentioned the possibility of dialogue, suggesting that it was not really about to launch war in response to routine protests by at most a few dozen people in Seoul, despite the anger they raised.
"If the puppet authorities truly want dialogue and negotiations, they should apologize for all anti-DPRK hostile acts, big and small, and show the compatriots their will to stop all these acts," KCNA cited the North's military as saying.
A South Korean Foreign Ministry spokesman later told a briefing the North Korean ultimatum was not worth a response and South Korea was waiting for the North to make a "wise decision".
Last week, the South's President Park Geun-hye offered talks but the North rejected the overture as a "cunning" ploy.
Park will meet U.S. President Barack Obama at the White House on May 7 to discuss economic and security issues, including "countering the North Korean threat", the White House said on Monday.
The United States has offered talks with the North, but on the pre-condition that it abandons its nuclear weapons ambitions. North Korea deems its nuclear arms a "treasured sword" and has vowed never to give them up.
Nevertheless, U.S. Secretary of State John Kerry, ending a trip to the region dominated by concern about North Korea, on Monday stressed his interest in a diplomatic solution.
A day earlier Kerry had appeared to open the door to talking without requiring the North to take denuclearization steps in advance. Beijing, he said, could be an intermediary.
North Korea has conducted three nuclear tests but it was not believed to be near weapons capability.
Missile launches and nuclear tests by North Korea are both banned under U.N. Security Council resolutions that were expanded after the North's February test.
The aim of the North's aggression, analysts say, is to bolster the leadership of Kim Jong-un, the 30-year-old grandson Kim Il-Sung, or to force the United States into talks.
The United States has 28,000 troops in South Korea.
A U.S. military helicopter crashed in a region near the border with North Korea on Tuesday with 14 people on board, all of them U.S. soldiers, South Korea's Yonhap news agency said.
There were no reports of injuries and the cause of the accident, which happened when the helicopter was landing, was being investigated, Yonhap said.