SEOUL, April 1 (Reuters) - North Korea's efforts to disrupt GPS signal reception in the South forced some fishing vessels to return to port on Friday, South Korea said, amid heightened tension over a recent nuclear test and rocket launch by its neighbour.
South Korea has been on high alert against possible cyber attacks from the North, after its angry rhetoric threatening war and further weapons tests in response to new sanctions imposed last month by the U.N. Security Council and the South.
On Thursday and again on Friday, South Korea said it detected signals sent from the North that it believed were intended to interfere with reception of signals from Global Positioning Satellite networks.
"The interference signal is confirmed to be coming from the direction of Haeju and Mount Kumgang," the South's telecommunications ministry said in a statement, referring to areas on the North's western and eastern coasts near the border.
About 70 of 332 fishing vessels that had left the South's eastern port of Sokcho on Friday returned early after suffering GPS malfunctions, Yonhap news agency said, citing the coast guard service.
Coast guard officials reached by telephone could not immediately confirm the report.
There have been no reports of air traffic disruptions, the South's transport ministry said.
The North has attempted similar disruption in recent weeks, officials said.
The Unification Ministry, which handles relations with the North, said it considered the activities as "provocation" which must stop immediately and that the North should "behave in a way more helpful to inter-Korean ties and to itself".
North Korea operates a wide range of equipment to disrupt GPS signals, and the South's military has a system in place to monitor such attempts, Yonhap quoted an unnamed South Korean military official as saying.
In March, South Korea's spy agency said the North had stepped up cyber attack efforts against the South, including a bid to break into a subway control system that was foiled.
South Korea has previously blamed the North for cyber attacks against its nuclear power operator.
The United States accused the North of a cyber attack against Sony Pictures in 2014, forcing the studio to cancel the scheduled release of a comedy film based on the fictional assassination of the country's leader.
The North has denied responsibility for the cyberattacks. (Reporting by Jack Kim and Hooyeon Kim; Editing by Clarence Fernandez)