Ukraine and other former Soviet states affected by the Chernobyl nuclear disaster are holding ceremonies on Saturday to mark the 22nd anniversary of the explosion.
Church services will be held throughout Ukraine in memory of the victims, and President Viktor Yushchenko will take part in a ceremony to lay flowers at the memorial to Chernobyl Heroes in Kiev.
The speaker of Russia's lower house of parliament, Boris Gryzlov, told reporters in Moscow: "Today we remember the events of 1986, the Chernobyl tragedy... We must always remember the heroism shown by those that took part in the liquidation of the accident and its consequences."
Vast areas, including beyond the Soviet Union, were contaminated by the radioactive cloud that spread after the explosion at the Chernobyl nuclear plant's fourth reactor.
For the anniversary, former residents of the 30-km restricted zone surrounding the plant have been allowed to re-visit the area, where abandoned ghost towns lie almost untouched since Soviet times.
The Chernobyl disaster was caused by overheating following a disastrous experiment involving fuel rods, which was ironically aimed at improving safety.
While the initial Soviet cover-up was condemned by the West, it is almost certain that the authoritarian regime in place at the time, which sent dozens of workers to their certain death in the operation to seal the damaged reactor, averted much greater loss of life using means that would have been inaccessible to an open, democratic society.
There is no accurate data on the number of deaths, due to Soviet secrecy over the disaster. The Chernobyl Forum said 56 people, mainly rescue workers, were killed at the scene, and another 4,000 died of thyroid cancer shortly afterwards.
Several million more people are believed to have been exposed to varying degrees of radiation.
More than 300,000 people were relocated. Some 5 million people live in areas of Belarus, Russia and Ukraine classified as "contaminated" by radioactive elements.
Ukraine has approved a new shelter to be built over the damaged reactor, and last year signed a contract with French contractor Novarka.
The giant arch-shaped steel casing is expected to cost $1.4 billion and will take five years to complete.
The current badly-worn protective shelter has been repaired and reinforced by Russian contractor Atomstroyexport, in a project funded by the international Chernobyl Shelter Fund comprising 28 countries and run by the European Bank for Reconstruction and Development.
Ukraine and other former Soviet states affected by the Chernobyl nuclear disaster are holding ceremonies on Saturday to mark the 22nd anniversary of the explosion.
