North Korea is spreading a GPS interference signal in South Korea’s border area, Seoul’s Ministry of Science, ICT and Future Planning said Thursday night.

The attack continued into Friday, and the ministry said the interference signal originated in the North Korean city of Haeju in the southwestern part of the country and the Mount Kumgang area, located in the southeastern side.

According to Seoul’s Ministry of National Defense (MND), the interference signal was detected at a weaker frequency for about a month and North Korea increased its strength from Thursday.

“The interference signal detected this time is between -80 to