Kyiv and Lviv, Ukraine CNN  — 

Russian forces have seized control of the Chernobyl power plant in northern Ukraine, the site of the world’s worst nuclear disaster, and are holding staff hostage, according to Ukrainian officials.

Troops overran the plant on the first day of Russia’s multi-pronged invasion of Ukraine, a spokesperson for the State Agency of Ukraine on Exclusion Zone Management, Yevgeniya Kuznetsovа, told CNN.

Alyona Shevtsova, advisor to the commander of Ukraine’s Ground Forces, said on Facebook that Russian forces have taken control of the power station and that the staff are being “held hostage.”

According to Mykhailo Podolyak, a Ukrainian presidential adviser, control of the Chornobyl zone was lost after a “fierce battle.”

Podolyak said the condition of the former Chernobyl power plant’s nuclear waste storage facilities is unknown.

“After a completely senseless Russian attack in this direction, it is impossible to say that Chernobyl is safe,” Podolyak added. “This is one of the most serious threats to Europe today.”

The White House on Thursday said it was outraged over “credible reports” that Russian soldiers are holding staff of the Chernobyl facilities hostage.

“This unlawful and dangerous hostage taking, which could upend the routine civil service efforts required to maintain and protect the nuclear waste facilities, is obviously incredibly alarming and greatly concerning,” White House press secretary Jen Psaki told reporters in a Thursday evening briefing.

“We condemn it and we request their release.”

Warnings over Russian moves

Earlier Thursday, Ukrainian President Volodymyr Zelensky warned that Russian forces were attempting to wrest control of the nuclear plant.

“Russian occupation forces are trying to seize the Chernobyl (nuclear power plant). Our defenders are sacrificing their lives so that the tragedy of 1986 will not be repeated,” Zelensky tweeted.”This is a declaration of war against the whole of Europe.”

The Ukrainian Foreign Ministry echoed the President’s warning, raising the specter of another nuclear disaster in the city.

“In 1986, the world saw the biggest technological disaster in Chernobyl,” the ministry tweeted. “If Russia continues the war, Chernobyl can happen again in 2022.”

Tourists are guided around the abandoned city of Pripyat, inside the Chernobyl exclusion zone, in 2019.

More than 30 people died in the immediate aftermath of an explosion that tore through Chernobyl’s No. 4 reactor on April 26, 1986, near Pripyat, Ukraine.

In the years that followed, countless others died from radiation symptoms, according to the International Atomic Energy Agency and the World Health Organization. The Ukraine government evacuated some 135,000 people from the area and the 19-mile exclusion zone around the plant will remain uninhabitable for decades.

In the months after the accident, a sarcophagus was built to cover Reactor 4 and contain the radioactive material. This later deteriorated, resulting in radiation leaks.

In 2016, a structure known as the New Safe Confinement was positioned over the sarcophagus. The huge, arched design is intended to prevent the release of contaminated material, as well as protect the sarcophagus from external impacts, such as tornadoes or extreme thunderstorms.

Russia launched a full-scale invasion of Ukraine before dawn Thursday with a series of missile attacks against locations near the capital Kyiv, as well as long-range artillery against the city of Kharkiv, near the Russian border. The assault quickly spread across central and eastern Ukraine as Russian forces attacked the country from three sides.

CNN’s Olga Voitovich, Sam Fossum, Tim Lister, Anastasia Graham-Yooll, Sam Romano, Julia Hollingsworth and Roman Tymotsko contributed to this report.