The presidential office of Cheong Wa Dae says the emergency alert system on the Imjin River failed to operate when a flash flood hit the area on Sunday.

Senior secretary of foreign affairs and security Kim Sung-hwan told a news briefing Tuesday that he was very sorry for the loss of six lives, adding that an early warning could have prevented the deaths.

He said the National Emergency Management Agency reported the incident to Cheong Wa Dae at 8:20 a.m on Sunday. At 12:24 p.m., the Joint Chiefs of Staff made another report but could not pinpoint the exact cause of the flood.

Kim added that Seoul demanded an apology from Pyongyang, as the North's earlier explanation on the incident was unacceptable. He said the government is mulling when to propose an inter-Koren meeting to discuss preventive measures with the North.