A U.S. Navy submarine has been steadily leaking radioactive water since June 2006, and has since stopped at three Japanese ports, Guam and Pearl Harbor, the U.S. government said Thursday.

U.S. and Japanese officials said the nuclear-powered sub, USS Houston, did not leak enough radiation to cause harm and would not hinder plans to station the USS George Washington in Yokosuka, Japan, Reuters reported.

"We do not think that the amount of leakage would have any impact on humans or the environment," a Japanese foreign ministry official told Reuters.

From June 2006 to July 2008, the Houston docked in Yokosuka, Japan, 30 miles southwest of Tokyo, and in the southern island of Okinawa and in Sasebo, 610 miles southwest of Tokyo, a U.S. statement said.

"The United States assures strict procedures and prevention systems for nuclear-powered warships coming into port, and Japan is also checking the radiation levels 24 hours a day," the foreign ministry official told Reuters.

The leak caused an uproar in Japan last week, with local residents and civic groups criticizing the foreign ministry for failing to disclose the leak promptly to the government and the public, Reuters reported.

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