Electronic jamming signals from North Korea which have affected scores of civilian flights in South Korea were continuing unabated on Thursday, officials said, amid simmering cross-border tensions.
"GPS (global positioning system) jamming signals are continuing this morning," Son Dong-Hwan, a transport ministry deputy director, told AFP.
As of 9:00 am (0000 GMT), a total of 319 aircraft had been affected since Saturday, he said. "But it poses no threat to navigational safety."
The state Korea Communications Commission said the signals were coming from a city just north of the border.
"We've traced the jamming signals to the direction of Kaesong," said Lee Kyung-Woo, a commission deputy director.
The transport ministry said aircraft had GPS signals jammed while flying over the central area of the Korean peninsula, or while taking off from or landing at Incheon or Gimpo international airports near Seoul.
Officials have said planes can instead use other navigation devices like the very-high-frequency omni-directional range (VOR) and inertial navigation systems.
The reason for the jamming, which the North has not admitted, was unclear but cross-border tensions are running high amid growing fears that Pyongyang may soon carry out a nuclear test following a failed rocket launch last month.
It was unclear how long the jamming of radio signals would continue. In recent weeks the North has frequently threatened offensive action against the South.
In March last year GPS jamming signals from the North lasted for 10 days during an annual US-South Korea joint military drill, Lee said.
Seoul's Yonhap news agency at that time said the jamming caused minor disruptions to military phones and navigational devices near Seoul.
In October 2010 the South's then-defence minister Kim Tae-Young said a Russia-made North Korean jamming device capable of disrupting guided weapons posed a fresh threat to security.
He blamed the North for intermittent GPS failures on naval and civilian craft along the west coast from August 23 to 25 that year.
North Korea in recent weeks has frequently threatened vengeance against the South for perceived disrespect while Pyongyang last month was celebrating the centenary of the birth of founding leader Kim Il-Sung.
The South is on alert for any border provocations. A South Korean nuclear expert said Wednesday the North had apparently finished preparations for such a test and was awaiting a political decision to go ahead.
In response to the launch the UN Security Council Wednesday ordered sanctions against three North Korean state firms said to have financed and organised the North's missile and nuclear programmes.© ANP/AFP