North Korea appears to have stopped jamming satellite signals in an apparent attempt to disrupt air and maritime traffic navigation systems in parts of South Korea, a high-ranking government source in Seoul said Tuesday.

The North has been blamed for global positioning system (GPS) disruptions that affected hundreds of commercial flights and ships in and out of South Korea since April 28, although no damage was caused as all had backup navigational systems.

"GPS jamming signals from North Korea have not been detected since May 14," the source said on condition of anonymity, adding the South's military is keeping "close watch" on the North's activities.

The source did not rule out the possibility North Korea could send such signals again.

The South's military is analyzing why North Korea sent the GPS jamming signals from its western border city of Kaesong, officials said.

The signal-scrambling may have been intended to "test electronic warfare devices by the North Korean military or block mobile phone signals inside the North," said an official at the South's military, who also spoke on the condition of anonymity.

"We are closely watching activities in military units in Kaesong where the signals were detected as originating," the military official said.

On Monday, President Lee Myung-bak and Chinese President Hu Jintao held talks in Beijing and pledged to cooperate closely to deal "more effectively" with North Korea, Lee's office said, as concern grows Pyongyang could stage additional provocations after last month's rocket launch.

The North's GPS attacks began after Pyongyang voiced anger at what it called insulting remarks made by South Korean leaders in connection with its failed rocket launch and costly birthday anniversary celebrations for late founding leader Kim Il-sung.

Lee estimated the costs of the rocket launch at US$850 million and said the North could have been better spent the money to feed its hungry people.

North Korea vowed retaliations, threatening last month to launch "special military actions" to reduce the Lee government to ashes in minutes. Seoul officials said the GPS attacks appear to be part of the North's latest threats.

Pyongyang has been blamed for jamming GPS signals in South Korea since 2010.

GPS is a satellite-based navigation system widely used by aircraft, ships and the military as well as private vehicle owners.

South Korean military fighters, cargo planes and precise guided bombs are not affected by the disruption of GPS signals as they are equipped with military-only satellite navigation systems, officials said. (Yonhap)