South Korea's President Moon Jae-in honored the victims of the pro-democracy Gwangju Uprising on Monday, speaking at the spot where protestors were killed 40 years ago.
Demonstrators protesting against military dictator Chun Doo-hwan confronted his martial law troops on May 18, 1980.
Official bodies 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 those who will remain will open up a better world. They were convinced that today's defeat will turn to tomorrow's victory".
"Those who survived fought for democracy to fulfill the yearnings of the dead."
But Gwangju remains one of the most politicized historical events in a heavily polarized country.
Some conservatives in the South continue to condemn the uprising as a Communist-inspired rebellion, while the left-leaning Moon -- who participated in other anti-dictatorship protests -- has reopened 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.
"The purpose is not to punish, but to record our history properly," Moon said.
"If you confess the truth now, it will open a path toward forgiveness and reconciliation."
The South is still technically at war with the nuclear-armed North and Moon's opposition seeks to paint him as a Pyongyang sympathizer, while attempting to use Gwangju to discredit liberals by linking them to the North.