Defense Secretary Lloyd Austin on Sunday condemned Russian President Vladimir Putin's annexation of four Ukrainian regions, warning there is no one to stop him from following through on his recent threats of using nuclear weapons.
"To be clear, the guy who makes that decision - I mean it's one man, there are no checks on Mr. Putin," Austin told CNN's Fareed Zakaria. "Just as he made the irresponsible decision to invade Ukraine, he could make another decision. But I don't see anything right now that would lead me to believe that he has made such a decision."
Facing territorial losses from a Ukrainian counteroffensive primarily in the country's northeast, Putin last month announced Russia would call up 300,000 reservists to bolster their military effort and threatened the West with nuclear weapons, saying it is "not a bluff."
"This nuclear saber-rattling is not the kind of thing that we would expect to hear from leaders of large countries with capability," Austin said on CNN.
The United States has vowed a decisive response if Russia moves forward with using nuclear weapons, and Biden administration officials say they have laid out the potential consequences for the Kremlin in more detail privately.
Austin on Sunday said he did not personally deliver that message but had previously relayed U.S. concerns to Russia's defense minister, Sergei Shoigu.
"Personally, I have not talked to Shoigu in recent days, but I have talked to him in the past," Austin continued. "And I have addressed this very issue and warned to not go down this path and conduct this type of irresponsible behavior."
Since Putin's speech to the Russian people to call up the reservists, the country illegally annexed Ukraine's Luhansk, Donetsk, Kherson and Zaporizhzhia regions.
The land grab came after Russia said residents supposedly signed off on the move in a referendum, although the vote was condemned by U.S. officials and the West as a sham.
Ukrainian forces, bolstered by funding and equipment from the West, have continued to dig in. Ukrainian President Volodymyr Zelensky vowed that Russia will not take new Ukrainian territory.
Over the weekend, Ukrainian forces took the key transportation hub of Lyman, a city located in the Donetsk region among those now claimed by Russia.
For the latest news, weather, sports, and streaming video, head to The Hill.