North Korea released water from a dam near its border with the South without warning early Wednesday morning, increasing fears of floods in areas already hit by heavy rainfall in recent days.
The North did not notify South Korean officials in advance of the floodgates opening.
Seoul has said it does not believe that Pyongyang would engage in a "flooding attack," but monitors water levels at the Hwanggang Dam closely.
No major injuries or damages have been reported from Wednesday's discharge, but South Korea has evacuated residents who live along the Imjin river.
Residents in areas prone to mudslides and flooding had been evacuated earlier this week following days of heavy rainfall.
Not first time
North Korea released water from the dam without warning in 2009, killing six South Koreans camping downstream. After that incident Pyongyang agreed to give notice before releasing water from the dam.
South Korea's Yonhap news agency says the North also opened the dam's floodgates twice in May without warning. No injuries were reported in either incident.
The North Korean dam is located about 42 kilometers north of the border and is believed to have a full capacity of about 300 million to 400 million tons.