Official remembrances have begun in Ukraine to mark the exact time of the Chernobyl nuclear disaster 20 years ago Wednesday.

Ukrainians are ringing church bells and holding candlelight vigils and moments of silence outside the abandoned nuclear plant and in towns across the country.

The opposition in neighboring Belarus has called for a protest today, accusing the Belarusian government of moving too slowly to clean up affected areas. Radioactivity from Chernobyl spread over a large part of Belarus.

Russian President Vladimir Putin Tuesday gave awards to workers who cleaned up the Chernobyl nuclear disaster.

President Bush issued a statement Tuesday, sending his condolences to those he says still suffer great hardships after the accident. He said that by closing Chernobyl more than five years ago, a free Ukraine removed an environmental threat built by an oppressive government in what was then the Soviet Union.

Twenty years ago, a reactor at the Soviet-built plant exploded, releasing a radioactive cloud across much of Europe. Experts say fewer than 50 people were directly killed by the blast and its radiation. The World Health Organization estimates the radiation will eventually cause fatal cancers in about 9,000 people worldwide. But the environmental group Greenpeace estimated the eventual death toll will be about 93,000.