"America and its allies are not going to be intimidated," Joe Biden said at the White House in reaction to Putin's words, BBC reported.
He then addressed the Russian president directly, saying, "America's fully prepared, with our Nato allies, to defend every single inch of Nato territory."
"Mr. Putin, don't misunderstand what I'm saying: every inch," the US president added.
Russian President Vladimir Putin held a speech before lawmakers in Moscow on the accession of the Lugansk, Donetsk, Kherson, and Zaporizhzhia regions.
The Kherson, Zaporizhzhia, and the Donbas republics will officially become part of Russia once lawmakers finalize legislation on their incorporation, and is signed by Putin.
The Kremlin has made clear that any attack on the newly annexed regions would be seen as an attack on Russian soil, signaling an escalation in the war.
MP/PR