Bolton, who was former President Donald Trump's national security adviser, spoke about the possibility of a nuclear war during an appearance on the British radio show LBC on Tuesday. He called on the U.S. to increase efforts to deter Putin from using nuclear weapons.

"We need to make clear if Putin were to order the use of a tactical nuclear weapon he would be signing a suicide note," Bolton said. "I think that's what it may take to deter him if he gets into extreme circumstances."

Bolton said he believes "making it clear we will levy responsibility" on Putin if he orders the use of nuclear weapons will increase the chances of deterring him from doing so. He added that he believes the U.S. is capable of targeting Russia's president.

"You can ask Qassem Soleimani in Iran what happens when we decide somebody is a threat to the U.S.," he said, referring to the Iranian military commander who was killed in 2020 by a U.S. airstrike in Iraq.