North Korea used jamming equipment to block South Korean military communication devices last week, a report said Sunday, amid high tension over the joint drills between Seoul and Washington.
Yonhap news agency said strong jamming signals sent across the border on Friday had caused minor disruptions to phones and navigational devices using GPS (Global Positioning System) at military units near the capital Seoul.
The signals are believed to have been sent from the North's military facilities in Haeju and Kaesong close to the heavily-fortified border, it said, citing Seoul intelligence and military officials.
South Korea's former defence chief Kim Tae-Young said Pyongyang was thought to have been behind the intermittent failure of GPS receivers on naval and civilian craft along the west coast during the joint military exercise between the South and the US last August.
The North's GPS interrupter is believed to be effective in preventing US and South Korean guided bombs and missiles from hitting their target accurately.