More than 800 people in northern Sweden may have cancer as a result of the fallout that spewed over the region after the Chernobyl nuclear accident in 1986, according to a new study by Swedish scientists.

The figure is significantly higher than any previous estimate, and the study drew immediate fire from critics who said they doubted the accuracy of the results.

The radiation was released on April 26, 1986, when reactor No. 4 at the Chernobyl nuclear plant exploded and caught fire, contaminating an area roughly half the size of Colorado. The accident forced the resettlement of hundreds of thousands of people and ruined some of Europe's most fertile farmland.

The study monitored cancer cases among the more than 1.1 million people in the northern parts of Sweden who were exposed to radioactive fallout. Researchers found that the cancer risk increased in areas with higher levels of fallout, which was spread by winds.

Of the 22,400 cancer cases among the group, 849 can be statistically attributed to Chernobyl, said Martin Tondel, a researcher at Linkoeping University who headed the study. The findings were first published in this month's issue of the Journal of Epidemiology and Community Health, a science magazine.

Leif Moberg, a radiation expert with the Swedish Radiation Protection Authority, questioned the findings. "The radiation dosage that we in Sweden got after the accident was too low to produce this many cancer cases," Moberg said, adding that it was probably too early to see any definite results of Chernobyl. "Most cancer cases don't develop until 20, 30 or 50 years later," he said.

Tondel said that although the increase in cases cannot directly be attributed to Chernobyl, he could not see any other explanation. "We've tried our best to explain it in other ways, but we can't," he said.