Thousands of North Korean troops and citizens rallied Sunday to slam the South Korean leader as Pyongyang again ramped up its hostile rhetoric against Seoul despite a surprise nuclear deal with the US.

The rally in the capital Pyongyang, which was broadcast live on North Korean television, saw protesters chant slogans inciting violence against the South Korean president including "Let's tear Lee Myung-Bak to death!". 

Participants, led by top military and communist party cadres, criticised Seoul for allegedly slandering the ruling Kim family and its perceived lack of respect during mourning for Kim Jong-Il who died in December.

Kim's son and successor Kim Jong-Un was not at the rally, which lasted for an hour.

The North's supreme military command threatened Friday to launch a "sacred war" against Seoul, accusing South Korean troops of displaying slogans or placards slandering the North's top leaders at military facilities. 

"We again declare to the world that we will launch indiscriminate and sacred war to wipe out the enemy traitors!" the North's military chief Ri Yong-Ho said in a speech during Sunday's rally.

Ri called the South's officials "mad dogs" and "psychos" and repeated a pledge to protect the North's new leader Kim Jong-Un, who took over from his late father, from potential attacks.

TV footage showed people marching at the vast Kim Il-Sung square, pumping fists in the air, chanting and holding giant portraits of Kim Jong-Il and his father -- the North's founding president after whom the square is named. 

Many held red flags and banners vowing "Merciless retaliation!" against the South and urging North Koreans to become "human bombs" to protect Jong-Un's regime. 

The rally follows a rare move last week by Pyongyang to engage with the US over its nuclear ambitions.

The impoverished communist state said last Thursday it would freeze some nuclear and missile activities in return for massive US food aid, in a breakthrough less than three months after the death of Jong-Il.

Following talks with US officials earlier this month, the regime also promised to allow UN nuclear inspectors to return, raising cautious hopes of eased tensions under its new young leader. 

But Pyongyang has since late last week issued a series of fiery statements towards Seoul, showing little change from its hostile tone since Jong-Un took power.

The North has vowed never to deal with the South's conservative leaders, accusing them of trying to spark a war and rejecting appeals for dialogue.

The North's foreign ministry said on Sunday the North's people were "full of hatred resentment" at the South's leader amid Seoul's ongoing joint military exercises with the US, which it says are war games for an invasion.

The state-run KCNA said more than 1.7 million young North Korean men have volunteered to join the army since Friday in a bid for "all-people revenge on South Korean human scum."

A spokesman of the South's unification ministry that handles cross-border affairs said Seoul had no official comment on the rally, adding that responding to criticism from Pyongyang does little to improve ties. (AFP)