Tokyo Electric Power (Tepco) , operator of Japan's wrecked Fukushima nuclear plant, said on Monday it is not clear if material found below the damaged No. 2 reactor at the site is melted nuclear fuel.
The utility inserted a camera under the reactor vessel and images from the probe showed black material coating a grating.
Tepco cannot rule out the possibility the material is uranium fuel that melted down in the 2011 disaster and will continuing analysing the photos and data, a spokesman told reporters at a press conference.
(Reporting by Yuka Obayashi; Writing by Aaron Sheldrick; Editing by Tom Hogue)