The world was on the brink of a nuclear accident at the Zaporizhia nuclear power plant on Thursday after the power outage at the two remaining reactors, President Volodymyr Zelenskyy said, Reuters reports.

The state nuclear company of Ukraine “Energoatom” said that fires in slag pits at a coal-fired power plant near the complex led to the disconnection of the reactors from the power grid. The company blamed Russian “occupiers” for the disconnection.

Zelensky, confirming earlier comments by an energy official to Reuters, said backup diesel generators were immediately operational to ensure uninterrupted power supply. Electricity is used for the cooling and safety systems of the NPP.

“If the diesel generators had not been started… if the staff of our station had not reacted after the power outage, then we would have already been forced to experience the consequences of the radiation accident,” he said in his video address to evening.

“Russia has put Ukraine and all Europeans on the brink of a radiation disaster.”

He also called on the International Atomic Energy Agency and other world organizations to act much more quickly to force Russian troops to leave the site of the largest plant of its kind in Europe.

If Zaporizhzhia NPP explodes, it will be a bigger disaster than Fukushima or Chernobyl

Russia recently carried out artillery and airstrikes in the Zaporizhzhia region, Ukraine’s General Staff says, where fighting near Europe’s largest nuclear power plant is raising fears of a catastrophic nuclear incident.

Last week, UN Secretary General António Guterres warned that any accident at the Zaporizhia NPP would be “suicide”.

Former world heavyweight boxing champion Volodymyr Klitsyko warned that fighting at the Zaporizhzhia nuclear power plant in Ukraine could lead to a much bigger disaster than those that took place in Fukushima and Chernobyl, dpa reported on Sunday, Agerpres reported.

Volodymyr Klytsiko, the younger brother of Kyiv Mayor Vitaliy Klytsiko and a former professional boxer, said it was unclear how Ukrainian personnel were holding up at the factory seized by Russian forces.

“The world must understand that if (the Zaporizhzhya NPP) explodes, it will have the consequences (of the Fukushima and Chernobyl disasters) several times over,” Volodymyr Klitsyko told the British Times radio station.

What happens without power?

In the event of a power outage, the plant will rely only on a backup diesel generator and will have no other options if it fails, said Petro Kotin, head of the Atomic Energy Company of Ukraine, the Guardian reported. After 90 minutes without electricity, the reactors reached a dangerous temperature.

“During this outage, the station will not be connected to any power source and this is the cause of the danger,” he said. “If you don’t provide cooling … within an hour and a half, the melting will already begin.”

The IAEA mission expected at the end of days

A mission of the International Atomic Energy Agency may go to the Zaporizhia nuclear power plant seized by Russia in the coming days, Ukrainian Energy Minister German Galushchenko said on Thursday, Reuters reports.

“The visit is planned. We are talking about the coming days – definitely no later than the beginning of September,” Galushchenko said in an interview with Reuters in Kyiv.

Earlier Dersatom of Ukraine reported that the nuclear plant was disconnected from Ukraine’s power grid.

Galushchenko told Reuters that it was extremely important that the IAEA mission could see what was happening at the station.