Japanese media have reported that the International Telecommunication Union issued a warning against North Korea regarding its recent GPS signal jamming detected from April through May.

Japan’s Kyodo News Agency said ITU Secretary-General Hamadoun Toure told Japanese media about the warning during a recent visit to the country.

The jamming of GPS signals can cause serious harm regarding aircraft safety and South Korea has filed reports to the ITU and urged the union to take action in order to prevent harm to South Korean aircraft and vessels from North Korean GPS signals.

No jamming signals have been detected from the North since mid-May.