Radioactive contamination has been found on external surfaces of a nuclear power station on the banks of major river in northeast Spain, the environmental group Greenpeace said Saturday.

Radioactivity linked to cobalt, manganese and other elements was detected on roofs, fences and other places around the Asco nuclear power station on the Ebro River 44 miles upstream from the Mediterranean Sea, Greenpeace said in a statement.

An accident with cooling liquid several months ago most likely caused a radioactive leak which has not been properly cleaned up, Greenpeace spokesman Mario Rodriguez told The Associated Press.

"The accident could have been due to a leak of radioactive material because of mechanical failure or faulty operation," Rodriguez said.

Greenpeace said in its statement that the source of the radiation "could be linked to highly radioactive water which had passed through a nuclear reactor during the last recharge of nuclear fuel in October 2007."

Radiation levels of more than five curies have been measured in several places around the plant, the statement said.

A call to the power station was answered by security staff not authorized to speak to the press and calls to the station's owners, power suppliers Endesa and Iberdrola, went unanswered.

The Ebro is, along with the Duero, Tagus and Guadalquivir, one of Spain's biggest and most important rivers.