New York, New York - US President Joe Biden said the world was at its highest risk of "Armageddon" since the 1962 Cuban missile crisis in comments at a fundraiser on Thursday amid Russia's war on Ukraine.

Biden said Russian President Vladimir Putin was "not joking" when he talks about potentially using nuclear, biological, or chemical weapons, according to his remarks as reported by the White House press pool.

Biden said he didn't think there was any way to use a tactical nuclear weapon and not end up with "Armageddon."

Russia recently annexed four Ukrainian regions, in a move that violated international law, and Putin said that Moscow would see Ukrainian attacks on those regions as attacks on Russia itself and would use all means to defend them.

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For some time now, Washington has been warning Moscow that the use of nuclear weapons would have serious consequences. The White House, however, has not commented publicly on what these consequences might look like.

The US government also said it had not seen any concrete steps taken by Russia to use nuclear weapons.

The Cuban Missile Crisis is considered by many to be the most tense period of the Cold War. The US and Soviet superpowers came the closest ever to a nuclear war in October 1962. The crisis ended when then US president John F. Kennedy promised not to attack Cuba and Soviet leader Nikita Khrushchev ordered the removal of nuclear weapons from Cuba.

Meanwhile, after a string of recent battlefield defeats, Moscow on Thursday said that Russian troops have taken a settlement in the Donetsk region of eastern Ukraine.

The village of Zaitseve had been brought under Russian control, Defense Ministry spokesperson Igor Konashenkov said in Moscow, adding more than 120 soldiers were killed on the Ukrainian side.

Moscow's claims could not be independently verified, and Ukraine has not confirmed Zaitseve's loss.

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The Russian army has reportedly come under criticism at home because Ukraine has been gaining ground and pushing back occupying forces in a counteroffensive launched in early September.

Last weekend, Russian troops gave up the strategically important city of Lyman.

Elsewhere, according to Konashenkov, Ukrainian soldiers repeatedly tried to break through the Russian defensive line in the north of the Kherson region, but were pushed back.

More than 100 soldiers of the Ukrainian army are said to have been killed. In addition, Russia claims to have destroyed six tanks and several armored vehicles.

Ukrainian President Volodymyr Zelensky said that "more than half a thousand square kilometers of territory and dozens of settlements have been liberated from the Russian sham referendum and stabilized only in the Kherson region" since the beginning of the month.

In his evening address on Thursday, Zelensky also said that Ukrainian forces also recorded successes "in the eastern direction."