TOKYO (Reuters) - Japan's nuclear crisis is slowly stabilizing and the country must now focus on repairing the damage wrought by the devastating earthquake and tsunami that struck the northeast coast a month ago, Prime Minister Naoto Kan said.
He was speaking shortly after new data showed more radiation leaked from the crippled Fukushima Daiichi nuclear power plant in the early days of the crisis than first thought.
That new information put Japan's nuclear calamity in the same category as the world's worst nuclear disaster, Chernobyl, officials said, but the upgrade in its severity rating to the highest level on a globally recognized scale did not mean the situation had suddenly become more critical.
"The situation at the Fukushima Daiichi plant is slowly stabilizing, step by step, and the emission of radioactive substances is on a declining trend," Kan told a press briefing.
"A month has passed. We need to take steps toward restoration and reconstruction."
He said he had instructed a reconstruction panel to create a work blueprint by June.
He also called on opposition parties, whose help he needs to pass bills in a divided parliament, to take part in drafting reconstruction plans from an early stage.
The government is considering spinning off the part of plant operator Tokyo Electric Power Co (TEPCO) that oversees the stricken facility, Jiji news agency reported on Tuesday.
TEPCO appears to be no closer to restoring cooling systems at the reactors, critical to lowering the temperature of overheated nuclear fuel rods. On Tuesday, Japan's science ministry said small amounts of strontium, one of the most harmful radioactive elements, had been found in soil near Fukushima Daiichi.
Hidehiko Nishiyama, a deputy director-general of the Nuclear and Industrial Safety Agency (NISA), said the decision to raise the severity of the incident from level 5 to 7 -- the same as the Chernobyl disaster in Ukraine in 1986 -- was based on cumulative quantities of radiation released.
No radiation-linked deaths have been reported since the earthquake struck, and only 21 plant workers have been affected by minor radiation sickness, according to Chief Cabinet Secretary Yukio Edano. Late on Tuesday, Edano said he was aware the upgrading of the severity classification would worry people.
"It doesn't mean the situation today is worse than it was yesterday, it means the event as a whole is worse than previously thought," said nuclear expert John Price, a former member of the Safety Policy Unit at the UK's National Nuclear Corporation.
Late on Tuesday, a senior official at the International Atomic Energy Agency (IAEA) said the latest data from food samples in 8 prefectures showed contamination below permitted levels.
Earlier, NISA said the amount of radiation released into the atmosphere from the plant, 240 km (150 miles) north of Tokyo, was around 10 percent that of Chernobyl.
"Radiation released into the atmosphere peaked from March 15 to 16. Radiation is still being released, but the amount now has fallen considerably," said NISA's Nishiyama.
Several experts said the new rating exaggerated the severity of the crisis.
"It's nowhere near that level. Chernobyl was terrible -- it blew and they had no containment, and they were stuck," said nuclear industry specialist Murray Jennex, an associate professor at San Diego State University in California.
"Their (Japan's) containment has been holding, the only thing that hasn't is the fuel pool that caught fire."
The blast at Chernobyl blew the roof off a reactor and sent large amounts of radiation wafting across Europe. The accident contaminated vast areas and led to the evacuation of well over 100,000 people.
Still, the increase in the severity level heightens the risk of diplomatic tension with Japan's neighbors over radioactive fallout. Chinese Premier Wen Jiabao told Kan on Tuesday he was "concerned" about the release of radiation into the ocean.
China has so far been sympathetic rather than angry, though it and South Korea have criticized TEPCO's decision to pump radioactive water into the sea, a process it has now stopped.
The March earthquake and tsunami killed up to 28,000 people and the estimated financial cost stands at $300 billion, making it the world's most expensive disaster.
Kan appealed to the Japanese people not to stop spending.
"I would like to ask the public not to fall into an excessive self-restraint mood and to live as normally as possible," he said.
Japan's economics minister warned the damage was likely to be worse than first thought as power shortages would cut factory output and disrupt supply chains.
Additional reporting by Risa Maeda, Yoko Kubota, Linda Sieg, Michael Perry, Paul Eckert and Nathan Layne in Tokyo, Chris Buckley in Beijing, and Ron Popeski in Singapore; Writing by Daniel Magnowski; Editing by Andrew Marshall