In 1997, the government designated the day as a national memorial day to mark the pro-democracy uprising in Gwangju, 329 kilometers south of Seoul, which left hundreds of people dead or missing due to the then military government's bloody crackdown.

But since 2009 during the conservative administration of former President Lee Myung-bak, the signature song has been sung by a choir, leaving ceremony attendees to choose whether to sing along or not.

In a departure from the nine-year practice, the song will become an official part of the ceremony starting this year, according to the Ministry of Patriots and Veteran Affairs.

Thursday's event is expected to bring about the largest number of participants ever estimated at about 10,000, it added.

The controversy over the song reflects the still-divided public sentiment about the May 18 uprising.

The movement is widely viewed as a key event in bringing about a pro-democracy victory in ending the authoritarian rule of former general-turned-President Chun Doo-hwan. But some conservative groups see it as an armed revolt against the government. (Yonhap)