North Korean broadcaster KRT shows soldiers and civilians in their thousands at a rally in Pyongyang.

About 150, 000 chanted slogans as North Korea underscored its threat to wage what it called sacred war against the South.

The target of their condemnation is South Korea's joint military exercises with the U.S. and the government of South Korean President Lee Myung-bak.

The rhetoric was uncompromising.

SOUNDBITE: North Korean Vice Marshal Ri Yong-ho saying (Korean):

"Our soldiers and civilians are full of hatred and resentment at the war games and the smell of gun powder by the Lee Myung-bak traitor group and the American imperialistic barefaced robbers."

Video provided to Reuters by the North's official KCNA news agency showed young North Koreans pledging to join or re-join the army if necessary.

That's in response to claims by the North that South Korean soldiers insulted its leaders by scrawling 'unspeakable defamatory words' on their portraits.

SOUNDBITE: Ri Song-ho, official of Central Committee of Youth League, saying (Korean):

"Our five million young people will never tolerate the great offence by the Lee Myung-bak traitor group and the military warmongers. We will follow them to the end and wipe them out."

North Korean state tv over the weekend showed footage of new leader army Supreme Commander Kim Jong-un visiting military units.

The visits took place in January.

It also aired photos of Kim visiting the truce village of Panmunjom.

The conflict between the two Koreas from 1950-53 ended only with a truce, not a peace treaty, leaving them technically still at war.

Some observers say the latest sabre-rattling is intended to consolidate Kim's grip on power at home.

They also suggest it's to gain an advantage in the latest round of disarmament-for-aid talks with the U.S.

Paul Chapman, Reuters