TOKYO - The operator of Japan's quake-struck Fukushima nuclear power plant said on Friday it could not rule out the possibility that it may still be leaking radiation into the sea.

A massive earthquake and tsunami in March 2011 triggered fuelrod meltdowns at the plant, causing radiation leakage, contamination of food and water and mass evacuations, although the government declared in December that the disaster was under control.

An aerial view shows Kansai Electric Power Co's Ohi nuclear power plant's No. 4 reactor (front) in Ohi, Fukui prefecture, in this photo taken by Kyodo July 19, 2012. [Photo/Agencies]

The comment by Tokyo Electric Power Co follows a US academic journal Science article that said high radiation levels in bottom-dwelling fish caught off Fukushima prefecture indicate continued radiation leaking from the Fukushima Daiichi nuclear power plant.  

Asked if Tokyo Electric, also known as Tepco, could confirm that the plant is not leaking radiation into the sea any more, a spokeswoman said: "Tepco cannot say such a thing, but we have confirmed that radiation levels are declining in both the sea water and seabed soil around the plant."

Ken Buesseler, senior scientist at Woods Hole Oceanographic Institution of the United States, said in his article on the Science website that little change in radioactive caesium levels found in Fukushima fish suggested a continued leak.

"The fact that many fish are just as contaminated today with caesium 134 and caesium 137 as they were more than one year ago implies that caesium is still being released to the food chain," he said.

Fishing off Fukushima prefecture, north of Tokyo, is prohibited except for test fishing for a few species such as certain types of octopus and squid, which are shipped only when they are found to be safe.