Mourners in Ukraine are marking the 22nd anniversary Saturday of the Chernobyl power plant disaster - the world's worst civilian nuclear accident.

Ukrainian President Viktor Yushchenko joined other top officials and mourners in Kyiv to lay flowers at a memorial to the victims.

To this day, questions remain about the overall toll of the disaster, which spread a radioactive cloud across large parts of the former Soviet Union and much of northern Europe.

The World Health Organization estimates that more than 9,000 people worldwide will eventually die from Chernobyl-related cancers. But the environmental group Greenpeace says the eventual death toll could exceed 90,000.

The ruins of the Chernobyl reactor hold 200 tons of nuclear fuel. The site is still dangerously radioactive, and a vast concrete sarcophagus built to enclose it, is deteriorating.

Plans to construct a new steel casing around the plant have yet to be completed.

Some information for this report provided by AP and AFP.