A U.N. aviation agency has expressed "grave concerns" over North Korea's attempts to jam GPS signals in the South and decided to send a letter to Pyongyang to warn against such activity that could cause serious safety problems, the foreign ministry said Thursday.

"The International Civil Aviation Organization held the 208th board meeting in Montreal, Canada, from May 16-June 17 and adopted the decision to send a warning to the North with regard to the GPS disruption issue," the ministry said in a press release.

"In addition, the ICAO board decided to send a letter in the name of its secretary general to the North to let the country know the results of the discussion at the meeting," it added.

South Korea said jamming signals were sent from five North Korean regions -- Haeju, Yonan, Pyonggang, Kumgang and Kaesong -- between March 31 and April 6.

GPS disruptions could cause mobile phones to malfunction and affect planes and ships that rely on the satellite signal for navigation. No damages have been reported so far.

About 1,000 airplanes from 14 countries reported GPS disruptions during the cited period, the ministry said. In May, Seoul raised the issue with the ICAO, demanding measures to prevent a recurrence.

The ministry said that the ICAO's latest decision is a "much stronger" response to the GPS jamming matter compared to the action taken by the organization back in 2012 when similar disruptions were reported, the ministry said. (Yonhap)