SEOUL/LONDON • South Korea has revived a project to build a backup ship navigation system that would be difficult to hack after a recent wave of GPS signal- jamming attacks it blamed on North Korea disrupted fishing vessel operations, officials say.

Global Positioning System (GPS) and other electronic navigation aids are vulnerable to signal loss from solar weather effects, radio and satellite interference and deliberate jamming.

South Korea, which says it has faced repeated attempts by the rival North to interfere with satellite signals, will award a 15 billion won (S$17.7 million) contract this month to secure technology required to build an alternative land-based radio system called eLoran, which it hopes will provide reliable alternative position and timing signals for navigation.

"The need for us is especially high, because of the deliberate signal interference by North Korea," a South Korean government official involved in the initiative told Reuters, requesting anonymity as he was not authorised to speak to the media.

The latest jamming campaign from the North began on March 31.

It lasted nearly a week and affected signal reception of more than 1,000 aircraft and 700 ships, originating from five locations along the border, South Korean officials said.

Aircraft traffic was not affected because the GPS is normally used as a backup, not a primary navigation tool, one of the officials involved in telecommunications policy said.

The jamming prompted warnings by South Korea's military to North Korea to stop what it called "provocation" and a protest at the United Nations (UN). North Korea has denied involvement.

South Korea has been on high alert against possible cyber attacks from the North following the North's nuclear and missile tests and threats of war in response to new sanctions imposed by the UN Security Council and the South.

The reclusive North and the rich, democratic South are technically still at war since their 1950-53 conflict ended in a truce, rather than a treaty. The North routinely threatens to destroy South Korea and its major ally, the United States.

Yesterday, South Korea warned there is a risk of its citizens being abducted by Pyongyang in retaliation for the defection of a dozen North Korean staff at a restaurant in China.

Twelve women working at the restaurant in the eastern Chinese city of Ningbo defected to the South with their manager last month.

Seoul said they came voluntarily while the North insists they were tricked into defecting by South Korean spies who effectively "kidnapped" them.

The South's Unification Ministry, which handles inter-Korea affairs, said overseas missions had been advised to heighten their vigilance.

REUTERS, AGENCE FRANCE-PRESSE