Kim made the comment in a speech Saturday at a military parade marking the 70th anniversary of North Korea's ruling party.
Kim did not specifically comment on the North's capabilities in nuclear weapons or long-range missiles in the speech, which was broadcast by the North's official Korean Central TV.
The parade kicked off what is expected to be one of North Korea's biggest celebrations ever - an attention-getting event that is the government's way of showing the world and its own people that the Kim dynasty is firmly in control and its military a power to be reckoned with.
Kim, clad in black, walked down a red carpet and saluted his honor guard. He then walked up to a podium and waved to the troops.
Visiting Chinese official Liu Yunshan stood clapping to Kim's left, with senior North Korean officials on Kim's right.
Kim smiled as he spoke with Liu through a translator.
The parade could hold some surprises for analysts abroad who will be watching its display of weaponry very closely, particularly North Korea's growing fleet of drone aircraft and long-range missiles.
The guest list is shaping up to be less impressive.While no world leaders were attending - North Korean ally China sent Liu, a senior Communist Party official, not its head of state, or even vice premier - the normally isolated and quiet North Korean capital has been flooded by tourists, international media and delegations ranging from ethnic Koreans living abroad to obscure Russian and Mongolian groups dedicated to studying North Korea's political ideas.
As the clock struck midnight Friday, Kim marked the anniversary by paying respect to both his late father and grandfather at the Kumsusan Palace of the Sun in Pyongyang, according to the North's official Korean Central News Agency, or KCNA.
Even though North Korean officials did not divulge details of the celebration plans, open-source satellite imagery has been monitoring large-scale troop activities at the Mirim military air base in Pyongyang, which has been rigged with a mock-up of Kim Il Sung Square.
Masses of Pyongyang citizens have for weeks been out in public plazas across the city practicing their roles for a torchlight parade in the evening.
For the finale, a stage has been set up on a river running through central Pyongyang for a late-night concert featuring North Korea's most popular musical group, the all-female Moranbong Band.
Tickets for foreigners hoping to attend the concert were going for 100 euros a pop.
The spectacle promises to be the most elaborate since Kim assumed power after the death of his father, Kim Jong Il, in late 2011, and the satellite imagery suggests the military parade could be the country's biggest ever.
Though military parades were out of fashion until about a decade ago, North Korea's leadership often uses anniversaries to rally the nation behind the military or the party, while at the same time reinforcing the primacy of the leader himself.
On Friday, senior state officials led a mass gathering in Pyongyang singing the praises of the party and the leader.
Also on Friday, Kim met with the Chinese delegation led by Liu Yunshan, the Communist Party's No. 5 leader, where Liu delivered a message by Chinese President Xi Jinping, KCNA said.
China's official Xinhua News Agency reported that Liu told Kim that China was willing to work with North Korea for a quick resumption of six-party nuclear talks.
The talks, which aim to end the North's nuclear program and also involve the U.S., South Korea, Russia and Japan, stalled seven years ago.
Some foreign analysts believe the particularly strong emphasis this year on making the anniversary of the party's foundation such a lavish fete is a sign that Kim is trying to build up his own stature along with that of the party relative to the military.
Though Kim's leadership and both institutions are strong, the power balance among various government organs in North Korea is a delicate one and maintaining that balance is a key to keeping Kim's regime solid and unchallenged.
North Korea maintains its "military-first policy," which it says is necessary to counter threats from South Korea and the United States, but officials have recently stressed the role of the party in improving the standard of living for the people, who are increasingly aware of how far they lag behind their affluent cousins south of the Demilitarized Zone and in economic giant China.
In the run-up to this year's anniversary, large-scale construction and development projects have been launched and hailed with great fanfare in the state media.
The projects include new hydropower plants and high-rise apartments, but it is unclear how much of North Korea's limited financial resources have been put into improving the lot of the majority of its citizens who are not fortunate enough to live in the relatively developed and affluent capital.
The US-Korea Institute said military units, which began mobilising in May, have been practicing at a mock-up of the venue for Saturday's parade and mass rally.
The institute's website 38 North said photos taken on Tuesday show about 800 tents, and more than 600 trucks and 200 armoured vehicles at a former air base in the east of Pyongyang.
The likely centerpiece of the parade, ballistic missile launchers, cannot be seen yet, but seven drones are visible on mobile launchers.
The parade is expected to be North Korea's biggest spectacle since Kim Jong-un took power in 2011.
It is not known if Kim himself will speak publicly at any of the day's events, though he did give reporters a surprise, close-up photo opportunity two years ago when the country held a similarly elaborate celebration for the 60th anniversary of the armistice that ended the 1950-53 Korean War.
To make sure everyone taking part in the spectacle knows their part, students, work units and other groups have filled public plazas for weeks to hone their marching, flag-waving and slogan-shouting skills.
On Thursday, crowds of students waving red flags and women in brightly colored traditional clothing could be seen in the area around the square. North Korean flags lined the streets.
"We are very proud of the 70th anniversary of the foundation of our party, it's an honor for us, and with this anniversary we will demonstrate our invincible single-hearted unity," said Chang Yong-ho, a student who will be taking part.
North Korea's leadership often uses anniversaries to rally the nation behind the military or the party, while at the same time reinforcing the primacy of the leader himself. The particularly strong emphasis on making the party foundation anniversary this year a lavish fete is also seen by some foreign analysts as a sign that Kim Jong Un is trying to build up the party's standing relative to the military.
Though both institutions are strong, the power balance among various government organs in North Korea is a delicate one and maintaining that balance is a key to keeping Kim's leadership solid and unchallenged.
Giving some credence to that argument, North Korean officials have recently stressed the role of the party in improving the standard of living for the people and a rocket launch that some foreign analysts expected to happen before the anniversary now appears to be unlikely.
"Our party sees the steady improvement of the people's standard of living as its main concern above everything else," professor Kim Chang-gyong, of the North Korean Association of Social Scientists, said in an interview with an Associated Press Television News crew. "Our party is now concentrating on building an economically powerful socialist state."
