Ukraine is marking the 30th anniversary of the Chernobyl nuclear disaster on April 26 with a memorial service and a series of events in remembrance of the world's worst-ever civilian nuclear accident.
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.
A memorial service was held shortly after midnight in the town of Slavutych, which was built to accommodate workers displaced by the Chernobyl disaster.
President Petro Poroshenko attended a ceremony on April 26 at the Chernobyl plant, which sits in the middle of an uninhabitable "exclusion zone."
In a speech, Poroshenko said that "the consequences of the catastrophe" have not been resolved.
He said the disaster had been "a heavy burden on the shoulders of the Ukrainian people" and that the country was "still a long way" from overcoming the tragedy.
The level of radioactivity remains high in areas around Chernobyl.
Since 2010, work has been under way to build a massive shelter over the damaged reactor and seal in about 200 tons of uranium thought to be still there.
There are fears that if parts of the damaged reactor collapse, another cloud of radioactive material could be thrown into the atmosphere again.