The report, published last September ahead of the 20th anniversary of Chernobyl on April 26 of this year, said fewer than 50 deaths had been directly attributed to radiation from the disaster, almost all of them exposed rescue workers.

It said the radiation from the world's worst nuclear accident could still cause up to 4,000 deaths in Russia, Ukraine and Belarus.

"These figures are an underestimation and completely false," the president of the German section of the US-based IPPNW, Angelika Claussen, told a news conference in Berlin.

Claussen said the exact number of victims would never be known.

But she said that IPPNW research had indicated that between 50,000 and 100,000 clean-up workers alone had died as of 2006, while up to 900,000 were permanently disabled.

Tens of thousands of children born in the Chernobyl region north of Kiev suffered birth defects and because of genetic mutation, the consequences for future generations could not be estimated.

And the IPPNW said the World Health Organization, which was cited in the UN report, predicted nearly 9,000 deaths in the future.

The group accused the UN nuclear watchdog, the International Atomic Energy Agency, of bias in its report because its official mandate is the promotion of nuclear power.

The IPPNW demanded "unlimited access" to official reports on Chernobyl, the end to nuclear power plants and long-term aid for people who have fallen ill as a result of the disaster.

Environmental watchdog Greenpeace accused the authors of the UN report of aiming to help Russia's nuclear lobby make its case for building new reactors, at a news conference in Moscow Wednesday.

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International Physicians for the Prevention of Nuclear War