Mykhailo Podolyak, an adviser to the Ukrainian presidential office, shared the news on Thursday, Reuters reports. The powerplant, which melted down decades ago, remains highly radioactive, and its capture raises questions about maintaining nuclear safety that can affect large swaths of the world. 

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

The Russian military appears to have been gathering around Chernobyl before Thursday, and Ukraine President Volodymyr Zelensky confirmed later in the day that Russian forces were attempting to seize the plant.

Chernobyl’s nuclear power plant, which is less than 12 miles from the Belarusian border, sits in the Chernobyl Exclusion Zone, a 1,000 square mile region with persistently high levels of nuclear radiation, stemming from the fallout of the power plant’s 1986 meltdown. The Ukrainian government has gone to great lengths to ensure the Exclusion Zone remains contained in the decades since.

A source in Russia told Reuters that claiming Chernobyl is intended to dissuade NATO and other western forces from engaging militarily with the Russian army.

Ukrainian officials have expressed concern that military action in Chernobyl could endanger the containment zone’s safety protocols.

“In 1986, the world saw the biggest technological disaster in Chernobyl,” Ukraine’s Ministry of Foreign Affairs tweeted. “If Russia continues the war, Chernobyl can happen again in 2022.”