Greenpeace said Tuesday in a new report that more than 90,000 people were likely to die of cancers caused by radiation from the Chernobyl nuclear disaster, countering a United Nations report that predicted the death toll would be around 4,000.

The differing conclusions underline the contentious uncertainty that remains about the health effects of the world's worst nuclear accident as its 20th anniversary approaches.

A reactor at the Chernobyl nuclear power plant in Ukraine exploded on April 26, 1986, spewing radioactive clouds over much of Europe. The fallout was particularly severe in northern reaches of Ukraine, western Russia and Belarus.

Areas immediately around the now-inoperative plant remain off limits, but people in other areas that received significant fallout are anxious about their health.

A report by the Chernobyl Forum — a group comprising the International Atomic Energy Agency and several other U.N. groups — last year said only 56 deaths thus far could be connected to Chernobyl and about 4,000 deaths total would ultimately be linked to the accident.

But Greenpeace, in a report citing data from Russia, Belarus and Ukraine, harshly disagreed and suggested the Chernobyl Forum report was deliberately misleading.

"It is appalling that the IAEA is whitewashing the impacts of the most serious nuclear accident in human history," Ivan Blokov of the environmental group's Russia office said in a statement. "Denying the real implications is not only insulting to the thousands of victims but it also leads to dangerous recommendations and the relocation of people in contaminated areas."

The Chernobyl Forum report had suggested that many of the health problems and complaints in the regions around Chernobyl were connected with unhealthy lifestyles, including heavy drinking and smoking, and with a culture of victimization.

Greenpeace countered that statistics from Belarus indicate there will be 270,000 cases of cancer attributable to Chernobyl radiation throughout the region and that 93,000 of those are likely to be fatal.

Greenpeace also cited a report by the Center for Independent Environmental Assessment of the Russian Academy of Sciences that found a sharply increased mortality in western Russia over the past 15 years, suggesting the rise was due to Chernobyl radiation.

"On the basis of demographic data, during the last 15 years, 60,000 people have died additionally in Russia because of the Chernobyl accident and estimates of the total death toll for Ukraine and Belarus could be another 140,000," Greenpeace's international office said in a statement.

The report also finds that "radiation from the disaster has had a devastating effect on survivors" other than cancer cases — "damaging immune and endocrine systems, leading to accelerated aging, cardiovascular and blood illnesses, psychological illnesses, chromosome aberrations and an increase of deformities in fetuses and children."