South Korea demanded an apology from North Korea over the sudden discharge of water from a dam that left six South Koreans dead or missing Sept. 6.

"With regard to the loss of our citizens' lives, our government demands a sufficient explanation from the North's responsible authorities and an apology," Unification Ministry spokesman Chun Hae Sung said in a statement, according to Yonhap news agency.

Seoul's demand for an apology came after Pyongyang explained in a written message Sept. 7 that an increase in the water level of the cross-border Imjin River had prompted it to release the water from the upstream Hwanggang Dam as an emergency measure.

Pyongyang promised it would issue alerts in the future to prevent similar incidents from happening, though it made a similar promise in 2005 after causing flooding in the South.