One of three workers severely injured in Japan's worst nuclear accident in September has died in hospital.

The death is the first in the history of the Japanese nuclear industry.

The man, Hisashi Ouchi, 35, died late on Tuesday, a Tokyo University Hospital spokesman said. Japanese media said the cause was multiple organ failure.

Mr Ouchi had been in a critical condition since the accident on 30 September at a uranium processing plant in Tokaimura, about 140 kilometres (90 miles) northeast of the capital. He received 17,000 times the normal annual exposure to radiation.

His condition had worsened since his heart temporarily failed in late November.

One of Mr Ouchi's colleagues, Yutaka Yokokawa, 54, was discharged from hospital on Monday, but is still receiving outpatient treatment.

His condition had been the least serious of the three.

A third worker, Masato Shinohara, 39, remains in hospital and doctors said on Monday that they did not know when and whether he would be able to leave.

Condolences

Prime Minister Keizo Obuchi offered sympathy to the dead man's family and promised to tighten nuclear safety.

"The government has been working so that such an accident will never be repeated," Mr Obuchi was quoted by Kyodo news agency as saying.

"We are determined to make further efforts to strengthen steps to ensure safety and prevent accidents."

The president of JCO, the company which operates the Tokaimura plant, also apologised for Mr Ouchi's death.

"I was praying for his recovery, but this is the worst situation. When you lose a precious life you can't mourn enough," Hiroharu Kitani was quoted as saying by Kyodo.

Government under fire

An investigation found that the men broke safety regulations by mixing dangerously large amounts of treated uranium in metal buckets, setting off a nuclear reaction.

Dozens of people were exposed to lower doses of radiation, while thousands living near the plant were forced indoors or were evacuated.

Accidents have plagued Japan's nuclear power industry, but the country relies on atomic energy for about one-third of its electricity.

The government has come under heavy fire for its lax supervision of the industry and its sluggish response to the Tokaimura accident.

Parliament last week passed a set of bills aimed at strengthening nuclear safety.