US forces kept 50 miles away from Japan nuclear plant

US forces in Japan are not allowed within 50 miles (80 km) of a crippled nuclear power plant, the Pentagon said on Wednesday, outlining a larger no-go zone than the one Japan has recommended amid fears about the spread of radiation.

Japan's government has asked people living within 12 miles (20 km) of the Fukushima nuclear plant to evacuate and those between 12 miles and 18 miles (30 km) to stay indoors to guard against dangerous doses of radiation.

Pentagon spokesman Colonel Dave Lapan said the larger no-go zone for the US military was a precaution and added it was not set in stone. Exceptions could be made, if necessary, with proper authorization.

Asked whether the US military might order troops to enter the no-go zone, or instead seek volunteers because of potential hazards, Lapan said: "No. But again, we're talking about the United States military."

"We train and equip all of our people to operate in all kinds of environments. So we know how to measure (radiation), we know how to test. We know how to respond. We know how to take precautions," he said.

Jappan's nuclear crisis appeared to be spinning out of control on Wednesday after workers withdrew briefly from a stricken power plant because of surging radiation levels and a helicopter failed to drop water on the most troubled reactor.

But the Pentagon described its safety measures as precautionary and said no US forces have shown signs of radiation poisoning.

Although more than 20 US personnel have been exposed to higher-than-normal doses of radiation, Navy officials have repeatedly said there was no risk to their health.

Still, the US Navy acknowledged it decided to reposition ships to safer waters farther from the power plant, even as it forges ahead with a massive US relief mission to help close ally Japan after its devastating earthquake and tsunami.

But it is the radiation emerging from the Fukushima nuclear plant in northern Japan that has caused the most alarm, including at two US naval bases in Japan where detection of radiation triggered a warning to Navy families living there to limit time outdoors and shut-off external ventilation.

One new precaution the military is taking is giving some flight crews potassium iodide tablets ahead of missions as a way to guard against effects of radiation.

The crews in question were departing from the Naval Air Facility Atsugi, which is about 150 miles (241 km) from the plant. Lapan said the precaution was taken because the crews might fly within 70 miles (112 km) of the plant.