"People's Army soldiers and the people will maintain war preparedness to the full to deal with US imperialists' manoeuvres for aggression," it said.
Kim's birthday is the biggest annual holiday in North Korea, marked by flower shows, dances, exhibitions and pledges of loyalty to the man credited with turning his country into a nuclear power.
Dozens of other events including a flower festival featuring displays of the "Kimjongilia" flower, artistic performances and sports competitions, have been staged to mark the day.
In the capital, Pyongyang, scores of North Koreans have lined up to lay flowers and salute at the giant bronze statue of his father, Kim Il-sung, the founder of North Korea who died in 1994.
"At the time of this significant February holiday I want to see president Kim Il-sung more than ever. That's why I've come to this statue early in the morning," Pyongyang resident Ri Un-ha, told the Associated Press.
|Kim Jong-il retains a tight grip on power but |
has yet to designate a successor [Reuters]
Kim Sang Jik, another city resident, said: "Every year on February 16 I want to see president Kim Il-sung and I feel pride of the revolution under our General. Whenever I come to this Mansu Hill I have a strong feeling to uphold our General as instructed by president Kim Il-sung."
To many North Koreans the elder Kim is known as the "Great Leader", while his son is referred to as "the General".
The celebrations come just a few days after the landmark six-nation agreement on North Korea's nuclear programme was signed in Beijing.
But comments from North Korean officials have given little indication that the leadership has changed its views on what it sees as the US threat facing the country.
|Kim has inherited the personality cult |
built by his father, Kim Il-sung [EPA]
At a meeting of party, government and military officials on the eve of Kim's birthday, Choe Thae-Bok, the speaker of North Korea's parliament, said the North's nuclear weapons helped maintain peace and security in Northeast Asia.
"The successful nuclear test last year represents a proud victory of Songun [military-first] politics, a historic event in the 5,000 years of the Korean nation and a thrilling demonstration of the greatness and might of the socialist DPRK [North Korea]," he said.
Choe said the North was closely watching with heightened alarm the US attempt to "stifle" it.
"Our army and the people will never sit idle should anyone dare attempt to hurt the sovereignty and diginity of the republic," he was quoted by the official news agency as saying.