Russian President Vladimir Putin’s threat to use nuclear weapons in Ukraine has brought the world closer to “Armageddon” than at any time since the Cold-War Cuban Missile Crisis, U.S. President Joe Biden said.

Putin celebrated his 70th birthday to a chorus of fawning praise from officials. But with his seven-month invasion unravelling, public events appeared more muted than just a week ago, when he staged a huge concert on Red Square to proclaim the annexation of nearly a fifth of Ukrainian land, Reuters reported.

In a clear repudiation of Putin’s record, the Nobel Peace Prize was awarded to Russia’s most prominent human rights group, Memorial, which Moscow has shut down over the past year. A Ukrainian human rights group and a campaigner against abuses by the pro-Russian government in Belarus were also awarded.

Ukrainian President Volodymyr Zelenskiy said Kyiv’s forces were swiftly recapturing more territory, including more than 500 sq km in the south where they burst through a second major front this week.

Russia’s failings on the battlefield have brought unusual public recrimination from Kremlin allies, with one Russian-installed leader in occupied Ukrainian territory going so far as to suggest Putin’s defence minister should have shot himself.

Biden said the prospect of defeat could make Putin desperate enough to use nuclear weapons, the biggest risk since U.S. President John Kennedy and Soviet leader Nikita Khrushchev faced off over missiles in Cuba in 1962.

“We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis,” Biden said in New York. “For the first time since the Cuban Missile Crisis, we have a direct threat to the use of nuclear weapons, if in fact things continue down the path they’d been going.”

Putin was “not joking when he talks about potential use of tactical nuclear weapons or biological or chemical weapons, because his military is, you might say, is significantly underperforming,” Biden said.

Concern so far has been over the prospect of Russia deploying a so-called “tactical” nuclear weapon – a short-range device for use on the battlefield – rather than the “strategic” weapons on long-range missiles that Washington and Moscow have stockpiled since the Cold War.

But Biden suggested it made little difference: “I don’t think there’s any such thing as the ability to easily (use) a tactical nuclear weapon and not end up with Armageddon.”

Russian Orthodox Patriarch Kirill, a vocal supporter of the war, led birthday tributes for Putin with a prayer for God to “grant him health and longevity, and deliver him from all the resistances of visible and invisible enemies”.

Ramzan Kadyrov, the leader of Chechnya, a once-breakaway region Putin reconquered in war 20 years ago, congratulated “one of the most influential and outstanding personalities of our time, the number one patriot in the world, President of the Russian Federation Vladimir Vladimirovich Putin”.

Ukrainian forces have advanced swiftly since bursting through the Russian front in the northeast at the start of September, and in the south this week.

Since Putin proclaimed the annexation a week ago, Ukraine has recaptured the main Russian bastion in northern Donetsk, and a swath of territory on the west bank of the Dnipro River in Kherson.

Ukrainian rescuers had retrieved 11 bodies and rescued 21 people from the rubble of buildings destroyed in missile attacks there, the State Emergency Service said in a statement. Reuters journalists saw bodies being carried out of the rubble.

Russia’s RIA news agency reported that a Ukrainian missile had hit a bus in the Russian-controlled city of Kherson, killing four and wounding three civilians.