Russian President Vladimir Putin came out swinging at the U.S. on Friday in an aggressive speech as he announced the annexation of four Ukrainian regions. 

In a message that was already expected to be hostile, Putin further escalated threats against Ukraine and the West by saying the U.S. set a "precedent" of nuclear warfare by hitting Japan with atomic bombs during World War II.

Fears have mounted since last week when Putin said he was "not bluffing" after he warned that Moscow would use "all weapons systems available" to defend Russian territory.

Putin

From left, Moscow-appointed head of Kherson Region Vladimir Saldo, Moscow-appointed head of Zaporizhzhia region Yevgeny Balitsky, Russian President Vladimir Putin, Denis Pushilin, leader of self-proclaimed of the Donetsk People's Republic and Leonid Pasechnik, leader of self-proclaimed Luhansk People's Republic pose for a photo during a ceremony to sign the treaties for four regions of Ukraine to join Russia, at the Kremlin in Moscow, Friday, Sept. 30, 2022.  (Dmitry Astakhov, Sputnik, Government Pool Photo via AP)

UKRAINE HAS 'ACCELERATED' NATO APPLICATION IN WAKE OF RUSSIA ANNEXING TERRITORIES, ZELENSKYY SAYS

In a speech to an audience that looked scared and resolute, Putin furthered these comments Friday and said all Ukrainian citizens living in the Luhansk, Donetsk, Zaporizhzhia and Kherson regions will now "forever" be a part of Russia and vowed to use "all available means" to protect them if those regions are attacked.

It remains unclear what type of attack would be viewed as an existential threat to Russia in those regions as brutal warfare has raged there since Russia invaded in February.

"It looks like he's in a very fighting spirit, the gloves have come off," Russia expert and former intelligence officer for the Defense Intelligence Agency, Rebekah Koffler, told Fox News Digital, describing the speech as "super aggressive."

"There's no way back it looks like for him. He is ready for the fight," she added. 

Koffler said Putin has readied the groundwork to, in his view, legitimately be able to deploy nuclear weapons in Ukraine as the threat of defeat mounts as the West – particularly the U.S. – deploy "superior" weaponry to Kyiv. 

putin nuclear

Russian President Vladimir Putin gestures during a ceremony to sign the treaties for four regions of Ukraine to join Russia, at the Kremlin in Moscow Friday, Sept. 30, 2022.  (Mikhail Metzel, Sputnik, Kremlin Pool Photo via AP)

RUSSIAN PRESIDENT VLADIMIR PUTIN ANNOUNCES ANNEXATION OF 4 UKRAINIAN TERRITORIES AFTER 'SHAM' REFERENDUMS

Koffler said Putin’s speech was "staged" in a manner that "was almost like a direct challenge to the West."

"He spoke directly not only to the Russian people, but also to [Ukrainian President Volodymyr Zelenskyy], to Ukraine," she added also noting Putin’s reference to the U.S. as Kyiv’s "real owners."

The Russia expert explained that Putin, a former KGB operative, is a "specialist" in manipulation and "pushed all the right buzzwords" in his speech by referring to historical figures like Catherine the Great to fire up his supporters at home.

"History has called us to a battlefield to fight for our people, for the grand historic Russia, for future generations," Putin said in his fiery speech.

Despite reports of a mass exodus of men fleeing Russia and nationwide protests following an order to send another 300,000 soldiers to fight in Ukraine, Koffler explained that Putin is surrounded by people who would support his use of nuclear weapons – no matter the cost of human life.

There is "a different relationship with life and the kind of sacrifices they are willing to tolerate," she said, adding that there is a sense of "pride" that Russia "can out-suffer the enemy."

Russian conscript

A Russian recruit speaks to his son prior to take a train at a railway station in Prudboi, Volgograd region of Russia, Thursday, Sept. 29, 2022. Russian President Vladimir Putin has ordered a partial mobilization of reservists to beef up his forces in Ukraine.  (AP Photo)

CLICK HERE TO GET THE FOX NEWS APP 

"Remember, in the beginning of this so-called special operation they let Russian forces march through the area around Chernobyl. It’s just a very different mentality," Koffler added. 

It remains unclear how the U.S. or its NATO allies would respond if Russian deployed a nuclear warhead in Ukraine.