The unification ministry has expressed regret over North Korea's discharge of water from its Hwanggang Dam without giving prior notice to the South.

A ministry official told reporters on Thursday that it is regrettable that the North opened the floodgates without prior notice, despite Seoul's request to Pyongyang last month, as previously agreed upon between the two Koreas in 2009.

The Ministry of Environment earlier said that it believes North Korea began releasing water from its Hwanggang Dam, located upstream of the Imjin River, late Wednesday night.

The environment ministry cited satellite images taken at 10 p.m. Wednesday, which showed no signs of discharge from the North's dam. But in images taken around 3 a.m. Thursday, it showed that the width of the Imjin River had gotten wider, signaling a dam water release.

While the ministry estimates that the amount of water discharged so far is not significant, it shared the situation with the military and local governments to activate an emergency response system to ensure the safety of nearby residents.