updated 8/2/2008 1:45:32 AM ET 2008-08-02T05:45:32

The U.S. Navy has warned Japan that a nuclear submarine may have had radioactive leaks during recent calls in two of its southern ports.

U.S. officials said the amount of radioactive water leaked was negligible, but the news could cause a stir in Japan, where both the U.S. military presence and its nuclear vessels are controversial.

Japan's Foreign Ministry said Saturday that the U.S. Navy had told it that the nuclear-powered USS Houston submarine might have leaked a small amount of radiation during port calls in the southern Japanese naval ports of Sasebo and Okinawa in March and April.

Sasebo city official Akihiro Yoshida said government monitoring during the submarine's calls showed no abnormal increase of radioactivity in the area's waters at the time.

"Still, we are rather concerned," Yoshida said.

Protests over aircraft carrier
News of the leak comes just weeks ahead of the controversial arrival of nuclear-powered aircraft carrier USS George Washington's in Yokosuka, just south of Tokyo.

The carrier's arrival was originally set for August under a Japan-U.S. security alliance, but it is being delayed until late September because of a fire aboard the vessel in May. The George Washington is relieving the soon-to-be decommissioned USS Kitty Hawk, and will be the first U.S. Navy nuclear-powered vessel to station permanently in Japan.

The George Washington's upcoming deployment had already triggered protests, and the fire escalated concerns many Japanese have about nuclear power.

Masahiko Goto, a lawyer representing a citizens' group opposing the George Washington's deployment in Yokosuka, sharply criticized the U.S. Navy for withholding information about submarine leak.

"They had discovered the radiation leak weeks ago and did not inform the Japanese government immediately," Goto said in a statement.

"The U.S. Navy's handling of the accident and lack of transparency showed there is no way we can trust them," he said.

Sensitive subject
In Japan, the only country to have suffered atomic bombings, many people are sensitive about military use of nuclear technology and the presence of American forces. The U.S. atomic bombings of Hiroshima and Nagasaki in August 1945 killed at least 200,000.

In Honolulu, U.S. Pacific Fleet spokesman Capt. Scott Gureck said Friday that the total amount of radioactivity released into the environment from the USS Houston at each stop was less than one half a microcurie — a negligible amount equivalent to the radioactivity of a 50-pound bag of fertilizer.

The Navy discovered the leak July 17 when a gallon of water spilled on a shipyard worker's leg from a valve while the submarine was in dry dock for routine maintenance at Pearl Harbor.

An investigation showed water may have been slowly leaking from the valve since March as the Los Angeles-class submarine traveled around the Pacific. But the Japanese Foreign Ministry said it was not known how long the USS Houston had been leaking the cooling water.

The Houston is based at Apra Harbor in the U.S. territory of Guam in the Western Pacific.

It visited a U.S. naval base in Sasebo in late March, and then stopped in Guam from late May to mid-June. The submarine sat in Pearl Harbor for about three weeks before it was dry-docked in mid-July.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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