Christian church leaders and decorated war veterans led the rally in downtown Seoul on a national holiday to mark a 1919 uprising against Japanese colonial rule.

Marchers burned a North Korean flag and said President Roh Moo-Hyun's policy of reconciliation with Pyongyang endangered national security.

German human rights activist Norbert Vollertsen floated a balloon containing a radio and food in a ceremony to draw attention to North Korea's dire famine and human rights problems.

North Korean sympathisers had gained too much influence inside Roh's left-leaning administration, according to some activists.

"We are very concerned about pro-North Korean leftists who have gained power in our society, threatening security," said Kim Chul-Ho, a 60-year-old ex-marine.

Banners called for a harder line against the communist state and improved ties with the United States.

"Block North Korea's nuclear weapons development through strong ties with the United States," read one banner as demonstrators chanted anti-Pyongyang slogans and waved US and South Korean flags together.

Two kilometers away, about 200 liberals held a rival rally supporting inter-Korean rapprochement and denouncing the United States and Japan for their tough stance toward North Korea.

North Korea also marked the anniversary with calls for a joint struggle by the two Koreas against Japan and the United States.

President Roh has vowed to pursue better ties with North Korea despite the 16-month-old nuclear crisis which has raised tension on the Korean peninsula.

In a speech marking the anniversary of the uprising, Roh urged an end to a rift between "left and right-wing" groups in South Korea.

"There should be no more conflict between left and right-wing groups," Roh said

He stressed South Korea should "embrace North Korea with a warm heart" despite its "eccentric" behavior.

Roh's government, elected on a wave on anti-US sentiment in late 2002, has opposed the imposition of sanctions or pressure on North Korea to force the bankrupt regime to scrap its nuclear weapons drive.

Roh's support base is among a younger generation of South Koreans who no longer view the North as a serious security threat to the South and oppose the continued presence of 37,000 US troops in South Korea more than 50 years after the end of the Korean war.

Conservative older generations see North Korea as a continued threat and the US troop presence as a deterrent.

"Our main enemy is Kim Jong-Il's troops in North Korea," said another banner, referring to the North Korean leader's 1.1 million strong army, the fifth largest in the world.

WAR.WIRE