The American defense secretary suggests that Russian President Vladimir Putin may not be bluffing when he threatens to use nuclear weapons in Ukraine.

Lloyd Austin commented after it was revealed that US officials had simulated alternative reactions to a nuclear escalation by Russia during the seven-month struggle.

Putin was accused of "nuclear sabre-rattling" last week when he threatened to deploy Russia's nuclear arsenal to defend Ukrainian land acquired during illegal referendums.

"There are no checks on Putin," Austin told CNN. "He made the irresponsible decision to invade Ukraine, he could make another decision."

The White House is considering responses such as isolating Russia from the global economy. According to The New York Times, a military reaction has been considered, although it would likely be a counterattack by Ukrainian forces using conventional weaponry supplied by the West.

According to US officials who talked with the newspaper, Putin is unlikely to employ nuclear weapons quickly. Instead, they hypothesized that Russia may launch a cybersabotage campaign across Europe, target top leaders in Ukraine, or target the country's infrastructure.

Putin's nuclear threat may be designed to intimidate the West into reconsidering its support for Ukraine or to force Kyiv to negotiate from a position of weakness.

A Ukrainian military source told The Times that they did not expect the West would respond with a nuclear bomb but instead would focus on stopping a Russian attack. As Ukraine attempts to reclaim the occupied territories, the coming weeks will be exceptionally perilous.

HR McMaster, who served as President Trump's national security adviser, stated that the nuclear threat was the "only quiver [Putin] has left" in light of Ukrainian military victories.

"I think the message to [Putin] is, if you use a nuclear weapon, it's a suicide weapon," he stated. "It should be taken seriously. We must, but we should not allow this to discourage our support for the Ukrainians."