Tokyo, Aug. 2 (Reuters): Water containing a small amount of radiation leaked from a US nuclear-powered submarine that stopped by Japan earlier this year, the US navy and Japanese government said today, prompting calls by civic groups for full disclosure.

The leak, which was too small to have any impact on the environment, was found during an inspection of the nuclear-powered Houston in Hawaii, the Japanese foreign ministry said, citing information provided by the US government.

“The amounts were very, very, very small and were not of the sort that would affect the human body or the environment,” chief cabinet secretary Nobutaka Machimura told a news conference.

The incident comes at a time when the US has been trying to allay fears over the planned stationing of nuclear-powered aircraft carrier George Washington in Japan, the only country to have suffered nuclear attacks.

A civic group opposed to the deployment of the George Washington said the leak raises doubts about the safety of the US navy’s nuclear-powered vessels.

“The claim...that the US navy’s nuclear-powered vessels are safe and are not susceptible to radiation leaks has completely broken down,” Masahiko Goto, a lawyer representing the group said in a statement. Goto called on the US navy to disclose the causes of the radiation leak.

Many Japanese are sensitive about the use of nuclear power by military forces.

The Japanese cities of Hiroshima and Nagasaki came under nuclear attack from the United States at the end of World War II in August 1945.

The radiation leak from the Houston came to light after an incident in July, when the submarine was in dry dock, Lieutenant Commander David Benham said.