Many will be old soldiers, now in their 70s and 80s, who fought in the US-led United Nations coalition against North Korean and Chinese communist forces in the war that still casts a dark shadow over the Korean peninsula.

The main ceremony will take place at the truce village of Panmunjom on the border with North Korea, where the armistice agreement was signed on July 27,

The accord established a buffer zone between North and South, the world's most heavily fortified border whose razor-wire and mine-strewn no-man's land serves as a symbol of the three-year conflict and its legacy of lasting division of the Korean people.

"This is not a celebration. This is a time for solemn memorial," said a South Korean Unification Ministry official, noting that 50 years after the fighting stopped, North and South Korea were still technically at war and the current nuclear crisis had driven tension on the Korean peninsula higher than at any time since the fighting stopped.

The armistice, essentially a ceasefire agreement between rival armies, was never replaced by a peace treaty and 37,000 US and some 700,000 South Korean troops face-off against North Korea's 1.1 million strong army over a border that remains a dangerous military flashpoint.

Communist North Korea, which says it has developed nuclear weapons in self-defense against what it claims are US plans to launch a second Korean war, has demanded the cancellation of all armistice agreement commemorations in the South.

Pyongyang, which commemorates the signing of the armistice agreement as a victory, said ceremonies at Panmunjom constitute a "very dangerous act, which demonstrates that another war may be enforced," in a protest letter to UN Secretary General Kofi Annan.

US-led forces were authorized by the UN to fight for South Korea after North Korea launched an invasion in June 1950. Sixteen countries supplied troops and a total of 21 lent support to the South. The North Korea advance was reversed and a two-year stalemate ensued after Chinese Communist forces were dispatched to Korea in support of Pyongyang.

Negotiations on the armistice agreement began on July 10, 1951 and continued through 500 meetings lasting two years and 17 days.

Since the armistice was signed, divisions over the past half century have hardened, and South Korea has evolved into a prosperous democracy while its Northern neighbour has slid into economic collapse, its people teetering on the brink of starvation.

"We walked away from the possibility of real peace and reunification 50 years ago at the end of the war. The two Koreas have grown further apart from each other in terms of political system, psychology and world view," said a Unification Ministry analyst

Efforts to reconcile the two sides following a summit in 2000 between former South Korean president Kim Dae-Jung and North Korean leader Kim Jong-Il have been dogged by the nine-month-old nuclear crisis.

Tension has grown since North Korea kicked out UN nuclear monitors and withdrew from the nuclear Non-Proliferation Treaty, insisting that it has a right to nuclear weapons to defend itself against US hostility.

A new breed of thinkers in South Korea sympathise with Pyongyang's view. They see the United States, rather than North Korea as the aggressor in the war, and blame Washington for the continued division of the peninsula.

Rising anti-US sentiment was notable late last year when hundreds of thousands of young South Koreans joined massive anti-US rallies, partly inspired by revisionist readings of the war and subsequent Korean history.

"Some blame South Korea and the United States for the war. There are deep divisions among South Koreans about what this all means. The armistice commemoration lays it all bare," said Park Soo-Gil, former South Korean ambassador to the United Nations.

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