North Korea has been celebrating the 101st anniversary of its founder's birth on Monday with no signs of tension easing on the peninsula.
The North earlier rejected talks with South Korea aimed at normalising ties and re-opening the joint Kaesong industrial complex.
The United States has also offered talks, but on the pre-condition that North Korea abandons its nuclear weapons ambitions. However, North Korea has vowed never to give them up, Reuters reports.
In the past month, the North has threatened to attack the United States, South Korea and Japan since fresh United Nations sanctions were imposed in response to its third nuclear arms test in February.
There has also been increasingly bellicose rhetoric from the North in response to joint military exercises being carried out by the US and South Korea off the Korean peninsular.
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.
However, officials discounted speculation that the North would proceed with a launch or a new nuclear test on the anniversary itself.
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.
Analysts say the aim of North Korea's aggressive acts is to bolster the current leadership of 30-year-old Kim Jong-un, the grandson of Kim Il-Sung, or to force the US to hold talks with the North.
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.
US envoy visits Japan
In Tokyo, United States Secretary of State John Kerry was meeting Prime Minister Shinzo Abe.
Japan also said it was willing for talks with North Korea if Pyongyang took steps toward de-nuclearisation.
Mr 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.
He 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.
