TOKYO - Early in the Fukushima nuclear crisis, U.S. officials felt that nobody in Japan's government was taking charge, and Washington considered evacuating American troops in a worst-case scenario, a retired U.S. envoy said Thursday.

When the March 11 earthquake and tsunami set off the crisis by crippling the Fukushima Dai-ichi plant and sending it toward meltdown, Prime Minister Naoto Kan's administration initially acted as if it was only the plant operator's problem, not the government's, former diplomat Kevin Maher said.

"There was nobody in charge. Nobody in the Japanese political system was willing to say 'I'm going to take responsibility and make decisions,"' said Maher, who co-ordinated U.S. help offered to help Tokyo deal with the crisis.

"Nothing was taking place at Fukushima Dai-ichi in terms of the government solving the problem" until about a week later when Tokyo and Washington launched a joint task force, he said.

The Japanese Prime Minister's Office said it had no immediate reaction to Maher's remarks about the government's management.

A former director of the U.S. State Department's Japan office, Maher had been dismissed for allegedly making insulting remarks about Okinawan people in an off-the-record talk with university students in December. But he was called back for duty on the task force when the crisis struck, and his retirement was postponed until April.

Maher co-ordinated more than 100 American nuclear, defence and other officials dispatched by Washington to work with the Japanese government as the reactors rapidly deteriorated.

Japan initially was not forthcoming with details of the crisis, while independent U.S. information indicated at least two of the plant's six reactor cores were melting down, he said.

"We were very worried about what was going to happen to Japan," he said, adding that U.S. officials drafted a plan to evacuate some of the nearly 50,000 Japan-based servicemen in a worst-case scenario involving plumes of radiation.

"The worst case scenario was, 'Would you have to move U.S. forces out of Japan if there were threat of radiation?"' he said.

"Fortunately that did not happen," he said, because such a pull-out could have caused a "tremendous negative impact" on the U.S-Japan security relationship.

Maher said he sympathized with Japanese evacuees forced to flee their homes in the communities around the plant due to leaking radiation, and expressed optimism that those communities could be cleaned up and restored.

"It can be done," he said, adding that it requires a huge expenditure and a very "decisive approach."