Concrete crumbling like sand, their faces burning red from the radiation. Sky News speaks to Chernobyl workers who did everything they could to prevent a second explosion forty years ago.

The memory of the accident at the Chernobyl Nuclear Power Plant in northern Ukraine continues to last 40 years after the tragedy, as a reminder of the importance of nuclear safety.

In the early hours of 26 April 1986, Reactor 4 at the Chernobyl Nuclear Power Plant exploded after a planned safety test went catastrophically wrong. The Chernobyl disaster was the result of a chain of critical errors — and its fallout was unprecedented.

On April 26, 1986, the Chernobyl nuclear reactor melted down, but the rest of the world wouldn't learn how close it came to nuclear Armageddon until weeks later.

Russia is 'again bringing the world to the brink of a man-made disaster,' declared the Ukrainian president, noting that Russian drones regularly fly over the Chernobyl plant and that one of them struck its protective shield last year.

Ukraine’s president lashed out at Russia, accusing it of “nuclear terrorism,” as Kyiv observed the 40th anniversary of the explosion at the Chernobyl power plant, the world’s worst civilian atomic disaster.

Photographs from the first days of the Chernobyl disaster and of the aftermath years later show the response, the evacuation and the long-term consequences of the world’s worst nuclear accident.

Nikolay Solovyov was on shift the night of April 26, 1986 when the Chernobyl nuclear power plant exploded. Instead of fleeing, he chose to fight his “first war” against radiation.

The BBC's Jessica Parker visits Pripyat, which was abandoned in 1986 after an explosion at the nearby Chernobyl nuclear power plant.