Ukraine had been urging the UN’s atomic energy watchdog to implement a safe perimeter around Zaporizhzhia and three other nuclear power stations in the country. 

But Western allies have refused to implement a no-fly zone, which would bring Nato into direct conflict with Russia. Senior defence sources said that while Ukraine still has a functioning air force that can strike at enemy convoys, a no-fly zone – repeatedly requested by Mr Zelensky – would risk a wider conflagration.

Nato signalled a change in policy from “deterrence” to defence after Jens Stoltenberg, the secretary-general, said more troops were likely to be sent to eastern European and Baltic states.

“We are now seriously considering a significant increase in that presence, both in more troops, with more air defence, with deterrence through defence,” he said.

Amid evident fears that a wider world war might be triggered accidentally, the Pentagon on Friday confirmed that it had established a new hotline with Russia’s ministry of defence to prevent “miscalculation, military incidents and escalation” in the region.

John Kirby, the Pentagon spokesman, said: “When we tested it they picked up and acknowledged they got the call. So we know it works. We think it’s valuable to have direct communication at an operational level to reduce risks of miscalculation and communicate in real time if need be.”

World leaders condemned the attack on the power plant at an emergency meeting of the UN security council. 

Linda Thomas-Greenfield, the US ambassador to the UN, said: “By the grace of God, the world narrowly averted a nuclear catastrophe last night. We all waited to exhale as we watched the horrific situation unfold in real time.”

She called on Putin to “stop this madness, and stop it now”. Russian forces, she added, “are now 20 miles, and closing, from Ukraine’s second-largest nuclear facility. So this imminent danger continues”.