South Korea said Wednesday it would send formal complaints to North Korea and to UN agencies, urging Pyongyang to stop sending GPS jamming signals that have affected hundreds of civilian flights.

The regulatory Korea Communications Commission will send a letter of complaint to Pyongyang while other agencies will contact the international organisations, the transport ministry said in a statement.

The South says the North began the jamming in late April, affecting the GPS signals of aircraft using Seoul's Incheon and Gimpo airports or flying over the central area of the Korean peninsula.

Shipping has also been affected. Seoul officials say air and sea traffic can use other navigational equipment and safety has not been compromised.

The North has not commented on the accusation, which comes at a time of high cross-border tensions.

"We will urge the North to immediately stop sending jamming signals and refrain from a recurrence," the ministry said, adding the signals were still coming from the North.

Seoul will complain to the International Telecommunication Union (ITU) and International Civil Aviation Organization (ICAO), it said.

"The act of jamming GPS signals... is against the ITU's constitution and poses a threat to the safety of international aviation operations guaranteed by ICAO rules," the ministry said.

The communist nation has previously been accused of GPS jamming.

In March last year officials said such signals lasted for 10 days during an annual US-South Korea joint military drill, causing minor disruptions to military phones and navigational devices near Seoul.

In October 2010 the South's then-defence minister Kim Tae-Young said a Russian-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.

The North has taken a hostile tone with the South since its young leader Kim Jong-Un took power in December following the death of his father Kim Jong-Il.

It has threatened "sacred war" against the South in retaliation for perceived insults during Pyongyang's commemoration in April of the centenary of the birth of founding leader Kim Il-Sung.

State media has described the South's President Lee Myung-Bak as a "rat" and "human scum" and called for his death.

The South's Foreign Minister Kim Sung-Hwan Wednesday described the level of recent threats as "very high" compared to the past.

"Therefore, we keep our guard up," he told a forum.