Defense Minister Kim Yong-hyun apologized Tuesday over the fate of members of a past secret unit that trained commandos to infiltrate into North Korea for the first time since they were killed more than a half century ago.

Kim's apology was read on his behalf during a ceremony to mark the beginning of an excavation project to find the yet-recovered remains of four Silmido unit members who were executed and secretly buried in 1972.

"May those who were sacrificed during the Silmido incident rest in peace, and I express deep apologies and condolences to bereaved family members for their suffering and sadness," the apology read, according to the defense ministry.

Unit 684, also known by the name of the Yellow Sea island where it was based, was created by the spy agency and the Air Force in 1968 after Pyongyang's failed attempt to attack the presidential office that year.

South Korea, however, never deployed the unit into action, according to the ministry.

The commandos, who underwent brutal training and unfair treatment, staged a mutiny and escaped the unit in 1971, but most of them were killed during a standoff with the military and police in southern Seoul.

A military court later sentenced the four survivors to death, and their remains are presumed to have been buried at a cemetery in Goyang, just north of Seoul.

The secret unit remained relatively unknown before the release of the 2003 film "Silmido" based on the story of its members.

In 2022, the Truth and Reconciliation Commission recommended an investigation into the burial sites and the excavation of the remains of the former members, as well as an apology to the victims. (Yonhap)