Russian forces have captured the Chernobyl nuclear power plant in Ukraine, a senior government official said on Thursday, according to Reuters.

“It is impossible to say the Chernobyl nuclear power plant is safe after a totally pointless attack by the Russians,” Mykhailo Podolyak, an advisor in the Ukrainian president’s office said. “This is one of the most serious threats in Europe today.”

Videos on social media showed Russian tanks at the power plant.

Earlier on Thursday, Ukrainian President Volodymyr Zelenskyy said on Twitter that Russian forces were trying to seize the decommissioned nuclear power plant. “Our defenders are giving their lives so that the tragedy of 1986 will not be repeated,” he said. “...This is a declaration of war against the whole of Europe.”

Zelenskyy was referring to the explosion at the power plant on April 26, 1986, which led to the worst nuclear disaster in human history. The plant was decommissioned after the disaster, and it later became a tourist attraction.

The Chernobyl exclusion zone was shut for tourists a week before Russia began its attack on Ukraine.

An advisor to the Ukrainian interior ministry, Anton Herashchenko, warned against fighting in the area around the nuclear power plant, according to Newsweek “If the invader’s artillery hits and ruins/damages the collectors of nuclear waste, radioactive nuclear dust can be spread over the territory of Ukraine, Belarus and the [countries] of the EU,” he said.

Russian President Vladimir Putin on Thursday launched a “military operation” against Ukraine. He insisted that Russia was left with no choice but to defend itself against what he claimed were threats emanating from Ukraine.

Zelenskyy, however, rejected Moscow’s allegation that his country posed a challenge to Russia and said that an invasion could lead to the loss of thousands of lives.

Russia and Ukraine have been engaged in a conflict since 2014 when Russia annexed Ukraine’s Crimean Peninsula and backed separatist rebellions in the country’s eastern regions of Donetsk and Luhansk.