SEOUL, South Korea (AP) — South Korea’s military said North Korea disrupted GPS signals from border areas for the second-straight day on Saturday, affecting an unspecified number of flights and vessel operations.

Tensions between the rival Koreas have escalated as North Korean leader Kim Jong Un flaunts his advancing nuclear and missile program and engages in electronic and psychological warfare, such as flying thousands of balloons to drop trash and anti-South Korean propaganda leaflets in the South.

South Korea’s Joint Chiefs of Staff said North Korean operations to manipulate GPS signals were detected from around the western border city of Kaesong and the nearby city of Haeju on Friday and Saturday, and said the activities disrupted dozens of civilian aircraft and several vessels.

While warning aircraft and vessels near western border areas, South Korea’s military did not specify how North Korea was interfering with GPS signals or detail the extent of disruptions.

“We urge North Korea to stop GPS interference provocations immediately and strongly warn that it will be held fully accountable for any resulting consequences,” the South’s joint chiefs said in a statement.