Russian President Vladimir Putin would only pursue the use of nuclear weapons in a situation wherein he sees an "existential threat" to the country or regime, according to a foreign policy expert and ex-Moscow official.

Former Russian foreign minister Andrei Kozyrev said in an interview with Fox News that if Russia feels threatened "in their hearts existentially" when NATO forces move into Moscow, that is the moment when Putin will "resort to nuclear weapons."

However, Kozyrev claimed that "there is no existential threat to Russia under present conditions."

After failing to seize Kyiv after a month-long campaign in northern Ukraine, Russia has shifted its strategy in recent weeks. The Russian military claimed to have completed phase one of its mission and would now focus on securing the Donbas region, which some have dubbed a "consolation" for the "sacrifice."

Putin's Latest Threat to NATO

Putin recently reaffirmed his nuclear threat after Finland and Sweden's announcements that they may apply for NATO membership in June when the current member nations meet in Madrid.

One of Russian President Vladimir Putin's closest allies warned NATO that if Sweden and Finland become members of the US-led military alliance, Russia will deploy nuclear weapons and hypersonic missiles in the European exclave of Kaliningrad, located between Poland and Lithuania.

According to Lithuanian Defence Minister Arvydas Anusauskas, Russia had deployed nuclear weapons in Kaliningrad even before its invasion of Ukraine started. He said that the international community is aware that "nuclear weapons have always been kept in Kaliningrad," and Russia uses it as a threat, as per an Al Jazeera report.

Dmitry Medvedev, deputy chairman of Russia's Security Council, said Moscow would bolster its land, air, and naval forces in the Baltic Sea if Sweden and Finland became NATO members.

Medvedev, a former Russian president, said that "the balance must be restored," and the Baltic region would no longer be "nuclear-free."

The Russian official expressed his hope that Finland and Sweden would be enlightened. They would have to live with nuclear weapons and hypersonic missiles close to home if they didn't, he warned.

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Zelensky Warns Nations To Prepare for Russia's Use of Nuclear Weapons

Meanwhile, in an interview with CNN, Ukrainian President Volodymyr Zelensky said that all nations must prepare for Russia's use of nuclear weapons in its attack on Ukraine.

He said that there is a chance that Putin will use nuclear or chemical weapons because he does not care about Ukrainian lives.

"Chemical weapons, they should do it, they could do it, for them the life of the people, nothing. That's why," Zelensky said.

However, the Ukrainian leader emphasized that the world should not be afraid, "be read" instead.

"But that is not a question for Ukraine, not only for Ukraine but for all the world, I think," Zelensky noted.

United States authorities have warned that if Putin is pressed against the wall, he may resort to using tactical nuclear weapons in Ukraine.

CIA Director Bill Burns said the US had seen no indication that Vladimir Putin is planning to take such action so far but that the agency is keeping a close eye on the possibility.

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