Russian forces started a fire on a nuclear power station in southern Ukraine to “blackmail” Kyiv as it pushes into Russian territory, Volodymyr Zelensky said.

A Ukrainian official said there was “unofficial” information that Russia on Sunday had set fire to a large number of car tyres on the cooling towers of the facility in Zaporizhzhia, which it occupied shortly after launching an invasion in February 2022.

Footage circulated on social media shows plumes of black smoke pouring off one of the towers.

While radiation is said to be at normal levels, it may have been a warning to Kyiv as it advances into Russian territory after launching a cross-border invasion on August 6.

Mr Zelensky, the Ukrainian president, accused Moscow of attempted blackmail and said it “must be held accountable” for the provocation.

“Currently, radiation levels are within norm. However, as long as the Russian terrorists maintain control over the nuclear plant, the situation is not and cannot be normal,” he wrote on X, formerly Twitter.

“Since the first day of its seizure, Russia has been using the Zaporizhzhia NPP [nuclear power plant] only to blackmail Ukraine, all of Europe, and the world.

“We are waiting for the world to react, waiting for the IAEA [International Atomic Energy Agency] to react.

“Russia must be held accountable for this. Only Ukrainian control over the Zaporizhzhia NPP can guarantee a return to normalcy and complete safety.”

The blaze broke out at a cooling tower “after an attack by the Ukrainian armed forces”, Vladimir Rogov wrote on Telegram after Kyiv blamed Russia for the incident.