North Korea's young new leader Kim Jong-un will likely order a third nuclear test or another missile launch later this year to boost his military image and consolidate his grip on power, a government think-tank in Seoul said on Wednesday.

The foreign ministry institute warned of military adventurism by the young Kim, and predicted the tests in the second half of this year or early 2013 around the time of the South's presidential election.

North Korea could raise tension by test-launching a missile and conducting a third nuclear test as Kim Jong-un needs to demonstrate his leadership and consolidate his grip on the regime, the Institute for Foreign Affairs and National Security (IFANS) said in the report.

The young Kim, named the great successor after his father Kim Jong-il's death last month, has focused quickly on promoting a hardline image to win the backing of the military.

Analysts say Kim is intent on proving he will stick by his father's songun, or military-first, doctrine, which steers most of the country's limited finances toward running the 1.2 million-strong army, even as much of the rest of the population goes hungry.

On Sunday -- a day believed to be Kim Jong-un's birthday -- state television broadcast a 50-minute documentary showing the new supreme leader mixing with generals and ordinary soldiers, driving a tank and brandishing a rifle.

In the video the then leader Kim Jong-il lauded his son's outstanding military strategies. He is quoted as describing him as a genius among geniuses.

The footage of the young Kim directing and mingling with military figures dated back to at least 2009, and coincided with a long-range rocket launch and second nuclear test in that year. Analysts say those tests were in some part planned by the young Kim and designed to shore up the military's support for his succession.

Video showed him shaking hands with officials at the launch site, and quoted him as saying he would have waged a real war if the enemies had shot down the rocket, which the North said was carrying a satellite.

Japan had threatened to shoot down any down any debris heading towards its territory.

The outside world viewed the launch as disguise for a test of a long-range missile, designed to reach Alaska States. It failed to enter orbit.

Washington warned last year that North Korea is becoming a direct threat to the United States and could develop an inter-continental ballistic missile within five years.

NUCLEAR TEST

The North is thought to have enough material from a plutonium programme to produce up to a dozen nuclear weapons. But it still does not have the technical ability to miniaturise and mount a nuclear warhead atop a missile.

The hermit state first tested a nuclear device in 2006.

The institute's report said the next nuclear test could use material from North's uranium enrichment facility, which the state unveiled in late 2010. Pyongyang says the programme is for peaceful, power-producing purposes.

Regional powers have for years tried -- with a mix of aid offers and punitive sanctions -- to stop Pyongyang's nuclear weapons programme which it argues is a necessary defence against a hostile United States and South Korea with which it still has no peace treaty to formally end the 1950-53 Korean War.

Analysts say it is highly unlikely the North will ever give up its nuclear ambitions as an atomic bomb doubles as the ultimate deterrent and bargaining chip in negotiations.

(Additional reporting by Iktae Park, Editing by Jonathan Thatcher)