PYONGYANG, North Korea — Army trucks loaded with artillery rolled by the memorial palace for North Korea's late leaders as Kim Jong Un presided over a military birthday commemoration for his father Thursday.

Kim Jong Il died of a heart attack in December, and North Koreans marked what would have been his 70th birthday by remembering him and showing support for his young son and successor.

Across Pyongyang, they bowed before Kim Jong Il's portrait and laid single blossoms in his honor on the holiday now called "Day of the Shining Star."

The Kim Jong Un ode "Footsteps" reverberated across the capital city all day, emphasizing the son's inheritance of the family legacy bequeathed to him by father and grandfather, North Korea founder Kim Il Sung.

The Kims have ruled North Korea since its inception in 1948 following the division of the Korean peninsula into the communist-backed north and the U.S.-allied south. Kim Il Sung remains the country's "eternal president" even after his death in 1994.

The transition to a third-generation Kim comes at a delicate time for North Korea, which struggles with a chronic food shortage and faces pressure to dismantle its nuclear weapons program.

The nation's leadership has leaned heavily on legacy in building up Kim Jong Un's credentials, highlighting the similarities to his grandfather in looks and style, and to his father in vision and policy.

"We're very proud to have him as a successor to Kim Jong Il. He's brimming with energy," said Jang Ye Song, a guide at a flower exhibition featuring Kim Jong Il's namesake red begonias. "We were completely charmed at the first sight of him."

Thursday's military show outside the Kumsusan mausoleum where Kim Jong Il's body lay in state reinforced Kim Jong Un's vow to uphold the "military first" policy that defined his father's rule.

Thousands of soldiers goose-stepped past the reviewing stand where Kim Jong Un stood, flanked by top military political leaders, beneath a massive portrait of Kim Jong Il.

As a military brass band played and fireworks exploded, tanks, trucks and jeeps filed by, loaded with artillery guns and rocket launchers. A sea of people waving red and pink plastic flowers blanketed the plaza outside the grandiose mausoleum.

"Bearing guns, we will faithfully uphold the 'military-first' leadership of our respected supreme commander and comrade," Ri Yong Ho, vice marshal of the Korean People's Army and the military's General Staff chief, said in a speech at the ceremony.

"Let's dedicate our lives to protect Kim Jong Un!" troops in the plaza roared.

The military show was nowhere near as extravagant as the massive parade at Kim Il Sung Square in October 2010 for the 65th anniversary of the Workers' Party of Korea, and an even bigger procession is expected for the April 15 celebrations that will mark the centenary of Kim Il Sung's birth.

But it was believed to be only the second military parade held at the memorial palace that once served as Kim Il Sung's presidential offices, and was seen as a fitting tribute to the late leader at a time when the nation is in a semiofficial state of mourning. Kim Il Sung's body has lain in state at Kumsusan since 1995, and his son's remains are expected to be displayed there as well.

Kim Jong Un was calm and composed as he saluted the troops. At times, he cracked a smile as he chatted with Ri Yong Ho and Armed Forces Minister Kim Yong Chun. Other key figures present were Kim Yong Nam, the president of the Presidium of North Korea's parliament; Premier Choe Yong Rim; Kang Sok Ju, a vice premier who was Kim Jong Il's key foreign policy adviser, and his aunt, Kim Kyong Hui.

Later, Kim attended a performance of songs and orchestral music in his father's honor at the Pyongyang Indoor Stadium that ended with a spirited rendition of "Footsteps" featuring tap-dancing soldiers. Afterward, the orchestra and performers stood to clap and chant "Kim Jong Un, single-hearted unity!" and "Kim Jong Un, defend to the death!" for five minutes, with the audience joining in.

Elsewhere in Pyongyang, at the main plaza at Kim Il Sung Square, the Pyongyang Circus Theater, the stadium and the Mansudae Art Studio grounds where a bronze statue of Kim Jong Il on horseback was unveiled this week, North Koreans paid their respects to Kim by bowing and laying flowers.

Among them was Paek Won Chol, who described himself as a "soldier and disciple" of Kim Jong Il. "I will devote my all for the building of a powerful and prosperous nation" under Kim Jong Un, he said.

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Thursday's memorial could serve as closure to North Korea's mourning ahead of important nuclear talks next week with the United States, said John Delury, an assistant professor at Yonsei University's Graduate School of International Studies in South Korea.

Kim Jong Il's death put discussions between Pyongyang and Washington on food aid and nuclear disarmament talks on hold. A U.S. envoy will meet with North Koreans next week in Beijing, the first such negotiations since Kim's death.

"There were a lot of balls in the air when Kim Jong Il died, so things froze," Delury said. "The timing of this public ceremony ... allows North Korea to make a last major public expression of grief as part of moving on and getting back to a lot of orders of business."

Associated Press writers Kim Kwang Hyon in Pyongyang and Hyung-jin Kim and Sam Kim in Seoul, South Korea, contributed to this report. Follow AP Korea bureau chief Jean H. Lee at twitter.com/newsjean and AP's chief Asia photographer David Guttenfelder at twitter.com/dguttenfelder.