Ukraine held memorial services on Tuesday to mark the 30th anniversary of the Chornobyl nuclear disaster.
A memorial service was held shortly after midnight in the town of Slavutych, which was built to accommodate workers displaced by the Chornobyl disaster.
Sirens were sounded in the early morning hours to mark 30 years since the moment that the first explosion blew the roof off the building housing a reactor and threw a cloud of radioactive material high into the air -- drifting across Ukraine's borders into Russia, Belarus, and across Northern Europe.
"The issue of the consequences of the catastrophe is not resolved. They have been a heavy burden on the shoulders of the Ukrainian people and we are still a long way off from overcoming them," said President Poroshenko attenting memorial ceremony.
More than half a million civilian and military personnel were drafted in from across the former Soviet Union as so-called liquidators to clean-up and contain the nuclear fallout, according to the World Health Organization.
Thirty-one plant workers and firemen died in the immediate aftermath of the accident, most from acute radiation sickness.