TOKYO – A U.S. nuclear-powered aircraft carrier to be stationed in Japan will send a 'strong signal' of Washington's commitment to defend its close ally, the commander of the U.S. military in Japan said on Thursday.

The USS George Washington is heading for a controversial berth south of Tokyo amid renewed concerns over North Korea's nuclear ambitions after Pyongyang took steps toward restarting an ageing nuclear plant that makes arms-grade plutonium.

The North has told the United States and the International Atomic Energy Agency of plans to restart its Yongbyon plant, and has moved stored equipment back to the reactor.

The United States has been trying to allay fears over the planned stationing of the aircraft carrier in Japan, the only country to have suffered nuclear attacks.

But a fire on board the warship in May and news last month that water containing a small amount of radiation had leaked from a U.S. nuclear-powered submarine that had stopped in Japan have renewed concerns.

Lieutenant-General Edward Rice said the fire, which blazed for 12 hours and seriously injured one sailor, had never posed a threat to the ship's nuclear reactor. The U.S. Navy has replaced the warship's captain as a result of the incident.

'I think when you peel the onion back on that one, you'll find that that should not pose any danger and should not constitute any reason why we should not station that carrier forward,' Rice told Reuters in an interview.

'It represents a tangible increase in capability over the ship that it replaces,' Rice said in his office at Yokota Air Base outside Tokyo.

Set to arrive in the Japanese port of Yokosuka south of Tokyo within weeks, the George Washington replaces one of the oldest active ships in the U.S. Navy, the USS Kitty Hawk.

'It provides one of the most visible and powerful deterrents and capabilities we can field and the fact that it is home-posted here in and of itself sends a strong signal of the United States' commitment to defend Japan that people and countries understand.'

AFGHAN HOPES

Rice also said it was too soon to abandon hope that Japan would renew its refuelling mission in the Indian Ocean in support of U.S.-led operations in Afghanistan, despite a deadlocked parliament and the prime minister's abrupt resignation on Monday.

Halting the naval mission risks irritating Washington, but Rice, while welcoming the operations to date, declined to predict what the actual impact would be.

'I think there is still an opportunity for them to renew the law that enables their refuelling mission, or to make some other decision to contribute,' he said.

Japan has been refuelling ships in the Indian Ocean to support U.S.-led military operations in Afghanistan since 2001, apart from three months late last year due to a battle in parliament over extending legislation authorising the mission.

Extending it again when the law expires in January will be hard with an opposition-dominated upper house able to block bills for months and the junior ruling coalition partner wary of upsetting voters by forcing the legislation through.

Many voters oppose the mission.

Prime Minister Yasuo Fukuda suddenly resigned on Monday over a political deadlock that is stymying policies from security to efforts to revive a faltering economy.

A new premier will be chosen later this month.

(Editing by Paul Tait)