Late last month, Putin renewed nuclear threats he made at the onset of Russia’s invasion.

“If the territorial integrity of our country is threatened, we will certainly use all the means at our disposal to protect Russia and our people,” the Russian leader said in a televised national address.

“I’m not bluffing,” he added.

Biden says he is taking Putin’s threat seriously, saying, “We’ve got a guy I know fairly well. He’s not joking when he talks about potential use of tactical nuclear weapons or biological or chemical weapons because his military is you might say significantly underperforming.”

“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,” he said.

The aggression comes as Russia continues to battle Ukraine, with hundreds of millions of dollars in additional aid sent to Ukraine. Russia recently took over four key territories in the country that used to be part of the former Soviet Union.