The U.S. aircraft carrier Ronald Reagan, whose home port is San Diego, has been ordered repositioned away from Japan's Fukushima nuclear power plant after low levels of radiation were detected in the air and flight deck, Navy officials said Monday.

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The maximum amount of radiation that crew members aboard the ship may have been exposed to was equal to that which someone might be exposed to during a month by natural sources, officials said.

The Reagan was operating about 100 miles northeast of the crippled plant as part of the U.S. humanitarian mission to the country, which was hit by a massive earthquake and tsunami.

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Low levels of radiation were detected among 17 crew members of helicopters ferrying supplies to the island. The contamination was "easily removed by washing with soap and water," officials said.

Still, the Reagan and two other San Diego ships, the Preble and the Chancellorsville, were ordered to move out the downwind direction from the nuclear plant and any leaking radioactivity. The U.S. remains committed to the relief mission, officials said.

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-- Tony Perry in San Diego

Photo: A Japanese Maritime Self-Defense Force helicopter aboard the carrier USS Ronald Reagan, which has served as a refueling platform for aircraft bringing supplies to a region ravaged by earthquake and tsunami. Credit: U.S. Navy