Ukraine has begun commemorations to mark the 30th anniversary of the nuclear disaster in Chernobyl.
Sirens were sounded at the same moment as the first explosion at the reactor, in the early hours of 26 April 1986.
The meltdown at the plant remains the worst nuclear disaster in history.
An uncontrolled reaction blew the roof off, spewing out a cloud of radioactive material which drifted across Ukraine's borders, into Russia, Belarus and across a swathe of northern Europe.
A memorial service was held in the town of Slavutych, built to re-house workers who lived near the nuclear plant.