South Korea's President Moon Jae-in honoured victims of the pro-democracy Gwangju Uprising on Monday, speaking at the spot where protesters were killed 40 years ago.

Demonstrators protesting against military dictator Chun Doo-hwan confronted his martial law troops on May 18, 1980.

South Koreans attend a ceremony marking the 40th anniversary of the pro-democracy Gwangju Uprising
South Koreans attend a ceremony marking the 40th anniversary of the pro-democracy Gwangju Uprising POOL / JUNG YEON-JE

Official organisations point to around 160 dead over the next 10 days -- including some soldiers and police -- and more than 70 missing, but activists say up to three times as many may have been killed.

Those who died, Moon said, "believed that the survivors would manage to open up a better world. They were convinced that the defeat of that day would become the victory of tomorrow".

South Korean President Moon Jae-in said 'Those who survived fought for democracy to fulfil the yearnings of the dead'
South Korean President Moon Jae-in said 'Those who survived fought for democracy to fulfil the yearnings of the dead' POOL / JUNG YEON-JE

The subsequent, successful struggle to establish democracy in South Korea had been in answer to "the call of the dead", he added.

But Gwangju remains one of the most politicised historical events in a heavily polarised country.

Official bodies point to around 160 dead -- including some soldiers and police -- and more than 70 missing, but activists say up to three times as many may have been killed
Official bodies point to around 160 dead -- including some soldiers and police -- and more than 70 missing, but activists say up to three times as many may have been killed AFP / Ed JONES

Some conservatives in the South still condemn the uprising as a Communist-inspired rebellion, while the left-leaning Moon -- who participated in other anti-dictatorship protests -- has re-opened investigations into the military's actions, including an alleged helicopter shooting incident.

Chun, who was convicted in 1996 of treason over Gwangju and condemned to death but released following a presidential pardon, remains hugely divisive and still denies any direct involvement in the suppression of the movement.

Moon has regularly highlighted Gwangju, and on Monday reiterated his call for it to be included in the country's constitution.

He backed a newly launched probe into the crackdown, urging those responsible for the "state-led violence" to come forward.

"Its purpose is not about punishment but about properly documenting history," Moon said.

"Instead, if those who are accountable show courage and confess the truth even now, the path to forgiveness and reconciliation will open up."

The South is still technically at war with the nuclear-armed North, and Moon's opposition seeks to paint him as a Pyongyang sympathiser, while attempting to use Gwangju to discredit liberals by linking them to the North.

South Korea Moon