Japan has voiced intentions to decommission a severely damaged nuclear power plant whose continued radioactive leaks have kept thrown the country into an unrelenting crisis since the March 11 earthquake and tsunami struck.

Four of the six reactors at the Fukushima Daiichi plant suffered extensive damage in the disaster.

Units 1, 2 and 3 are believed to have experienced a partial meltdown, and Unit 4 has seen its spent fuel rods directly exposed to the air, a troublesome scenario that has called forth a worldwide reflection on nuclear safety.

Given the grave picture, the crippled nuclear power plant must be scrapped, Prime Minister Naoto Kan said Thursday, a day after Chief Cabinet Secretary Yukio Edano said the Fukushima plant was highly likely to be decommissioned.

Edano said at a news conference Wednesday that he believed that all the six reactors at the nuclear facility in northeastern Japan should be shut down for the best interests of the Japanese public.

At a separate news conference on Wednesday, Tsunehisa Katsumata, chairman of Tokyo Electric Power Co. (TEPCO), operator of the Fukushima nuclear plant, said the company plans to deactivate at least four of the six reactors.

Due to the nuclear accident, which was not expected to end anytime soon, TEPCO, Japan's largest utility firm, faces a reduced power generation capability, huge compensation liabilities, and thus a gloomy future. Nationalization has been tabled as an option.

Citing "significant financial obligations," rating agency Moody's on Thursday downgraded TEPCO by three notches.

Meanwhile, flanked by visiting French President Nicolas Sarkozy, the Japanese prime minister said Thursday that nuclear power is at the top of the agenda of the May summit of the Group of Eight industrialized economies.

Sarkozy, for his part, said that the summit will release a communique on nuclear issues, while adding that atomic power will remain a viable source of energy as the world needs it to cut carbon dioxide emissions.

No need to expand evacuation zone

Meanwhile, Japanese authorities on Thursday rejected calls for expanding the 20-km evacuation zone around the radiation-leaking nuclear power plant, but promised a swift response if the situation continued to worsen.

The decision was announced after the International Atomic Energy Agency (IAEA) on Wednesday urged Japan to expand the off-limits zone after radiation levels detected at a village some 40 km from the Fukushima nuclear complex were found to exceed recommended levels.

"We have no plans to immediately evacuate people, but naturally, high radiation levels in soil, if continued over a long period of time ... if need be, (we will) take steps to deal with it," Edano said Thursday.

Meanwhile, Japan's nuclear safety agency said that the level of radioactive iodine in the sea near the ravaged nuclear plant had surged to a new high of 4,385 times the legal limit.

"We will do our utmost to stop it from rising," said Hidehiko Nishiyama, a spokesman of the Nuclear and Industrial Safety Agency, adding that the contaminated water posed no immediate threat to human health.

In a call for international assistance in taming the nuclear emergency, he said, "the amount of water is enormous, and we need any wisdom available."

Experts from French nuclear giant Areva, which supplied fuel to the plant, are helping figure out how to dispose of the contaminated water that has begun leaking into the ground and the sea.

"We are not a supplier only for happy days," CEO Anne Lauvergeon told reporters in Tokyo on Thursday. "We are effectively also there when things become difficult."

A team of 140 U.S. military members specializing in radiation control also will also visit Japan soon, according to Japan's Kyodo news agency.

In addition, IAEA head Yukiya Amano said Thursday that the agency would send more sea experts to Japan.

Concerns about the persisting nuclear crisis have largely overwhelmed those about the March 11 twin natural disasters, which police said had left 11,417 people dead and 16,273 others unaccounted for by Thursday.