He lamented continued reckless remarks by some politicians and scholars to distort or play down the truth behind the historic event, officially named the Gwangju Democratization Movement.

"As a Korean, I feel tremendous shame when facing the reality of preposterous remarks denying and insulting the May 18 Democratization Movement still being uttered out loud without any hesitation," he said in a speech at the ceremony held in the city, 268 kilometers south of Seoul.

Earlier this year, three lawmakers with the conservative main opposition Liberty Korea Party (LKP) came under fire for publicly describing the Gwangju uprising as a riot, linking it with North Korea or insulting the bereaved families of the victims.

More than 20 years ago, Moon said, "We already reached a national consensus in this way about the historic significance and nature of the May 18 Gwangju Democratization Movement and brought relevant legal matters to a close."

"No more controversies about this issue are necessary now. They would simply be a meaningless waste," he stressed. "The truth about the May 18 movement cannot differ between conservatives and liberals."

He emphasized it was aimed at protecting freedom and democracy, saying only "the would-be heirs of a dictatorship" would see it in a different way.

The junta dispatched tank-led paratroopers to crack down on the nine-day uprising, initiated by college students and later joined by many other citizens. More than 200 people were killed and 1,800 others wounded.

Moon pointed out, "Much more remains to be done to reveal the truth with regard to those in charge of the massacre, secret burials of victims, sexual violence and the firing on protestors from helicopters."

He stressed: "Our task now is to uncover the truth that has yet to be clarified. This will allow us to put down the heavy historical burden that Gwangju has so far shouldered and turn the May of tragedy into the May of hope."

Last year, South Korea introduced special legislation, which revolves around the creation of a fact-finding committee. It has yet to be launched amid a political controversy over members.

"I urge the National Assembly and those in politics to take on this task with a greater sense of responsibility," the president said.

The LKP head Hwang Kyo-ahn also attended the ceremony in the face of a strong protest by a group of activists.

They tried to block Hwang from joining the event, claiming he should first take severe disciplinary measures against the lawmakers who made thoughtless comments on the May 18 uprising.

More than 5,000 people, including the leaders of other political parties, were present at the ceremony.

(Yonhap)