South Korea confirmed on Monday that North Korea has been trying since Friday to jam communications signals across the border, where the US and South Korea are holding a major joint military exercise.According to the Korea Communications Commission, signals are being emitted from near the North's border city of Kaesong to disrupt navigational devices using GPS, the Global Positioning System, northwest of Seoul. Intermittent GPS disruptions are still continuing, although signals are weak, the Commission said in a statement, adding that it was working with government agencies and security authorities to counter the jamming. It was not clear whether the disruption caused problems to the war games.