North Korea celebrated the 101st anniversary of its founder's birth on Sunday with no signs of tension easing on the peninsula after it rejected talks with South Korea aimed at normalising ties and re-opening a joint industrial park.
The United States has also offered talks, but on the pre-condition that North Korea abandons its nuclear weapons ambitions. North Korea deems its nuclear arms a "treasured sword" and has vowed never to give them up.
The North has threatened for weeks to attack the United States, South Korea and Japan since new UN sanctions were imposed in response to its latest nuclear arms test in February.
South Korea's defence ministry said it remained on guard against a possible new missile launch to coincide with the Day of the Sun, the date state founder Kim Il-sung was born. But officials discounted speculation that the North would proceed with a launch or a new nuclear test on the anniversary itself.
"North Korea is not believed to have launched a missile on the occasion of the Day of the Sun, of which today's is the 101st," ministry spokesman Kim Min-seok told a briefing. Read: Despite tension, North Korea lets in tourists, athletes
"But the military is not easing up on its vigilance on the activities of the North's military with the view that they can conduct a provocation at any time."
Kim Il-sung was born in 1912 and led his country from its founding in 1948, through the 1950-53 Korean War and until he died in 1994. His son, Kim Jong-il, then took over. Read: North Korea in holiday mode amid missile fears
The South Korean unification ministry, which oversees relations with the North, said it was "regrettable" that the North had rejected an offer of talks, made last week by President Park Geun-hye. It said the offer would remain on the table.
Missile launches and nuclear tests by North Korea are both banned under UN Security Council resolutions, that were expanded after its third nuclear test, in February.
The aim of the North's aggressive acts, analysts say, is to bolster the leadership of Kim Jong-un, 30, the grandson of the reclusive state's founder, or to force the United States to hold talks with the North. Read: Looking for logic in North Korea's cycles of threats
Third in family dynasty
The third Kim to rule in Pyongyang attended a midnight celebration of his father and grandfather's rule with top officials, including his kingmaker uncle Jang Song-thaek and the country's top generals.
In Tokyo, US secretary of state John Kerry was meeting Prime Minister Shinzo Abe after making a weekend offer to hold talks with the North if it abandoned its nuclear weapons programme. Read: US open to negotiations with North Korea: Kerry
Japan also said it was willing for talks with North Korea if Pyongyang took steps toward de-nuclearisation.
Kerry's trip to South Korea, China and Japan was aimed at reassuring its allies and putting pressure on Beijing to act decisively to implement the UN sanctions.
Kerry said he believes China, the North's sole economic and political benefactor, should put "some teeth" in efforts to persuade Pyongyang to alter its policies.
The Chinese Communist Party mouthpiece, the People's Daily, warned on Monday that tensions could get out of control.
"Bad things will always happen if a bowstring is drawn for too long," the paper wrote in a commentary.
"It does not matter if it is intentional or accidental, even the smallest thing could cause the situation to change rapidly and perhaps get totally out of control." Read: UK varsity slams BBC for covert N Korea trip
If matters did go out of control, it said, "no party will be able to stand on the side".
North Korea has repeatedly stressed that it fears the United States wants to invade it and has manipulated the United Nations to weaken it. At the weekend, the North rejected the overture by new South Korean President Park as a "cunning" ploy.
"We will expand in quantity our nuclear weapons capability, which is the treasure of a unified Korea ... that we would never barter at any price," Kim Yong-nam, North Korea's titular head of state, told a gathering of officials and service personnel applauding the achievements of Kim Il-Sung. Read: Burger selling aunt controlling North Korea's Kim Jong-un?
Kim Il-Sung's birthday is usually marked with a mass parade to showcase the North's military might. In 2012, following the death of his father, Kim Jong-un made a public speech, the first in living memory for a North Korean leader.