Radioactive leakage from fuel rods at a nuclear power plant in the city of Tsuruga in Fukui prefecture on Honshu island of Japan are believed to be the cause of a surge in the density of toxic substances detected in coolant water, the prefectural government said Monday.

Japan Atomic Power Company, owner and operator of the potentially faulty nuclear plant, has said it will attempt to manually override the plant's No. 2 reactor's system in an effort to contain the leak and conduct further investigation into its critical cooling systems.

The utility firm operating the 1,160-megawatt No.2 reactor at its Tsuruga nuclear plant cited "technical difficulties" at the reactor and while claiming there had been no radiation leak did confirm a possible leak of iodine from the reactor's nuclear fuel assemblies into its coolant system, adding a new saga to the nation's ever-unfolding nuclear crisis.

While intensive fact-finding continues, experts are drawing similarities with leaking fuel assemblies which sparked an ongoing nuclear crisis in Fukushima prefecture, following the partial meltdown of nuclear fuel rods in assemblies at quake and tsunami- damaged reactor buildings at Tokyo Electric Power Company's No. 1 nuclear plant in Fukushima prefecture.

Among cities on the Japan Sea coast, Tsuruga is the nearest city to the Pacific Ocean and is well known for its seafood trade.

But the coastal region has been plagued with nuclear problems, including in December 1995 when a sodium leak caused a major fire and forced an emergency shutdown.

However, the details were withheld from the public in a massive cover-up and according to official sources, reports were falsified, videotape footage taken immediately after the accident was edited and a gag order was issued to the plant's employees.

Tsuruga, which hosts 15 nuclear reactors is known in Japan as Genpatsu Ginza (Nuclear Ginza) due to the number of nuclear facilities along its Wakasa Bay corridor.

The name derives from the upscale Tokyo shopping district that boasts many large department stores crammed into a relatively small area.