Ukraine claimed on Friday that Russian President Vladimir Putin had “ordered the preparation of a terrorist attack” on the Chernobyl nuclear power plant. The main electric supply to the plant — site of the 1986 explosion and meltdown that traumatized the world — was cut off on Wednesday, with Ukrainian authorities blaming Russia’s invading forces for the blackout and warning that it could lead to “nuclear discharge.” 

A Ukrainian national emergency services agency said if power to the plant’s cooling systems — which keep spent nuclear fuel safely surrounded by water — is not ensured, it could create a “radioactive cloud” that would blow over “other regions of Ukraine, Belarus, Russia and Europe.”

The U.N.-backed global nuclear watchdog agency, the IAEA, downplayed concerns of an imminent radioactive release, saying the spent fuel was old enough and there was enough water around it in the cooling tanks to prevent a disaster, even without power. The IAEA and Ukrainian officials said backup diesel generators at the site would also be able to keep vital systems running for two to three days.

On Thursday, Russia claimed the power supply cable had been restored by a team of engineers who crossed into Ukraine from Belarus, but the IAEA and Ukrainian officials said work to repair the line was still ongoing.

Then came the warning from Ukraine’s Defense Intelligence Agency that “a man-made catastrophe is planned at the Russian-controlled Chornobyl NPP [Nuclear Power Plant], responsibility for which the occupiers will try to shift to Ukraine.”

CBS News is seeking information on the alleged plot by Russia from U.S. officials and the IAEA. American and European officials have warned for many weeks, even before Putin ordered the invasion of Ukraine, that the Russian leader could seek to stage “false flag” attacks to blame on Ukraine as a pretext for military action.

The Ukrainian government said in its Friday statement that Chernobyl remained completely disconnected from IAEA monitoring systems and was “de-energized,” noting, two days after the power cut, that the “service life of the available diesel generators is designed for 48 hours of maintenance of safety systems.”

Russian forces in control of the plant “refused to grant access to the station to Ukrainian repair people,” Ukraine’s Ministry of Defense said in the statement on Friday. Among the engineers sent from Belarus, it claimed, were Russian “saboteurs” pretending to be nuclear scientists who came “to organize a terrorist attack.”

Russian forces quickly seized the Chernobyl site after launching their invasion on February 24. Ukrainian officials have said the team of plant operators who ensure safe operations at the decommissioned facility have tried to continue carrying out their work, but under the orders of Russian troops and without being allowed to leave the compound at all.

Russia has since captured another of Ukraine’s nuclear power plants — a fully functioning one and the largest in Europe.   

All normal modes of communication between Chernobyl and the Ukrainian government have been cut.

A State Department spokesperson told CBS News on Friday that the U.S. condemned Russia’s seizure of the Chernobyl plant and called on Russian forces to immediately withdraw from all of Ukraine’s nuclear facilities and allow power and safe working conditions to be restored.

“Russia knows the importance of being a responsible nuclear power, and it should act like one,” the spokesperson said, calling the country’s actions “profoundly irresponsible and dangerous.”

Asked on Thursday about concerns over safety at Chernobyl, U.S. Director of National Intelligence Avril Haines told the Senate Intelligence Committee that the U.S. “should be concerned, but we haven’t yet seen anything that takes us from concerned to ‘it’s a complete crisis.'”  

Matt Kroenig, who worked on both nuclear and Russia related issues under the Bush, Obama and Trump administrations, told CBS News senior investigative correspondent Catherine Herridge this week that Putin was weaponing Ukraine’s civilian nuclear facilities as part of a strategy to terrorize, and potentially to stage a major nuclear event.  

“It may be a nuclear threat without resorting to the use of [nuclear] weapons,” said Kroenig. “If there were to be an accident at these plants, it could be quite serious. We’ve seen serious accidents in the past at Chernobyl and Fukushima, and so I think that may be part of the strategy here, of holding the plants at risk and making people worry about a potential nuclear disaster.”

Short of initiating an actual nuclear disaster, Kroenig said Putin may also be using his forces’ control of both Chernobyl and Ukraine’s sprawling, still-functioning Zaporizhzhia nuclear power plant to “terrorize the Ukrainian people and the world more broadly” as his military invasion was suffering unexpected delays as it closed in on Ukraine’s major cities.

“The worst-case scenario,” said Kroenig, a former CIA officer who’s currently deputy director of the Atlantic Council’s Scowcroft Center for Strategy and Security, “is that you could have a nuclear meltdown.”

If the cooling systems at Chernobyl are allowed to fail, “the nuclear core could literally melt down so that radioactive material could melt, it could get into the Earth’s crust, could get into the water supply… so this is potentially a serious ecological disaster.”

Kroenig did not go as far as to suggest that Putin could stage an attack on one of Ukraine’s nuclear facilities, but he said Putin’s actions could lead to a major nuclear event.

Any deliberate attack on a nuclear power plant would constitute a war crime under the Geneva Conventions, a series of laws signed by all United Nations member states, including Russia, that regulate acts of war.