(CNN) Russian President Vladimir Putin announced the immediate "partial mobilization" of Russian citizens on Wednesday, a move that threatens to escalate his faltering invasion of Ukraine following a string of defeats that caused recriminations in Moscow.
Putin said in a speech that he would use "all the means at our disposal," and even raised the specter of nuclear weapons, if he deemed the "territorial integrity" of Russia to be jeopardized.
The mobilization means citizens who are in the reserve could be called up, and those with military experience would be subject to conscription, Putin said, adding that the necessary decree had already been signed and took effect on Wednesday.
Defense Minister Sergei Shoigu said on Russian television Wednesday morning that the country will call up 300,000 reservists. "These are not some people who have never heard of the army," Shoigu said. "These are those who have served, have a military registration specialty, have had military experience."
It comes after a sudden and successful Ukrainian offensive through most of occupied Kharkiv swung momentum in the conflict back towards Kyiv this month. The counter-attacks galvanized Ukraine's Western backers and caused anger in Russia, which has time and again been stymied in its full-scale assault of its neighboring state that it launched seven months ago.
"Our country also has various means of destruction and in some components more modern than those of the NATO countries, and if the territorial integrity of our country is threatened, we will certainly use all the means at our disposal to protect Russia and our people," Putin said in his speech Wednesday indicating a possible new chapter in the months-long conflict.
Addressing the potential for escalation and use of nuclear weapons, Putin said: "Those who try to blackmail us with nuclear weapons should know that the prevailing winds can turn in their direction."
The announcement comes as Russia is believed to face shortages of manpower and follows amendments to Russia's law on military service made Tuesday, which raise the penalties for resistance related to military service or coercion to violate an official military order during a period of mobilization or martial law.
Putin framed the ongoing fighting as part of a larger struggle for Russian survival against a West whose goal is it is to "weaken, divide and ultimately destroy our country." Several Russian-occupied regions of Ukraine announced that they will hold referendums on formally joining Russia this week, votes that have widely been dismissed as shams intended to boost Putin's justifications for further attacks on Ukrainian territory.
"They are already saying directly that they were able to split the Soviet Union in 1991 and now the time has come for Russia to break up into a multitude of regions and areas which are fatally hostile to each other," Putin said.
But NATO leaders dismissed the announcement as a sign of panic in the Kremlin, and reaffirmed their commitment to supporting Ukraine's military.
US President Joe Biden condemned the mobilization and the Kremlin's planned votes, during his speech to the United Nations General Assembly on Wednesday.
"Just today, President Putin has made overt nuclear threats towards Europe ... now Russia is calling up more soldiers to join the fight, and the Kremlin is organizing sham referenda to try to annex parts of Ukraine," Biden said. "The world should see these outrageous acts for what they are.
"Putin claims he had to act because Russia was threatened, but no one threatened Russia -- and no one other than Russia sought conflict," Biden added.
German Chancellor Olaf Scholz meanwhile called the mobilization an "act of despair."
"Russia cannot win this war. But this is a kind of panic reaction," Dutch Prime Minister Mark Rutte added Wednesday.
The referendums, which Putin backed during his speech Wednesday, could pave the way for Russian annexation of the areas, allowing Moscow to frame the ongoing Ukrainian counteroffensive there as an attack on Russia itself, thereby providing Moscow with a pretext to escalate its military response.
In what appeared to be a coordinated announcement, Russian-appointed leaders in the occupied regions of Kherson and Zaporizhzhia and the self-declared Luhansk People's Republic and Donetsk People's Republic all said they planned to hold "votes" beginning on September 23.
Together the four regions that have announced their referendum plans make up around 18% of Ukraine's territory. Russia does not control any of the four in their entirety.
The expected referendums, which run counter to international law upholding Ukraine's sovereignty, have been announced as world leaders have descended on New York for a meeting of the United Nations General Assembly, where the war and it impacts were already poised to loom large.
Ukraine has dismissed the announcement of referendums in the occupied regions as a "sham" stemming from the "fear of defeat," while the the country's Western supporters signaled they would not alter their support for Ukraine.
US Ambassador to Ukraine Bridget A. Brink wrote on Twitter Wednesday that "sham referenda and mobilization are signs of weakness, of Russian failure. The United States will never recognize Russia's claim to purportedly annexed Ukrainian territory, and we will continue to stand with Ukraine for as long as it takes."
Putin on Wednesday said Russia has been asked for support from the two "people's republics" and the regions of Kherson and Zaporizhzhia for the referendums and had pledged to do "everything to ensure the safe conditions for people to express their will."
The announcements had already received swift support from Russian politicians. Former Russian President and vice-chairman of Russia's National Security Council Dmitry Medvedev has publicly endorsed referendums in the self-declared Donbas republics, saying this would have "huge significance" for "systemic protection" of the residents.
"Encroachment on Russian territory is a crime which allows you to use all the forces of self-defense," Medvedev said on his Telegram channel, in an apparent allusion to the potential for the military escalation.
But social media video geolocated by CNN showed protests in several Russian cities on Wednesday, each involving what appear to have been a few dozen people. The independent monitoring group OVD-Info said that more than 100 people had been detained at anti-mobilization demonstrations in total.
It's unclear what form an escalation could take, but concerns have been raised throughout the conflict over whether Russia would resort to using its nuclear stockpile in the Ukraine.
US President Joe Biden addressed these concerns in a 60 Minutes interview earlier this week, when a reporter asked what he would say to the Russian leader regarding the use of chemical or tactical nuclear weapons.
"Don't. Don't. Don't. You will change the face of war unlike anything since World War II," Biden said, adding that the US response to such actions would be "consequential."
Putin endorsed a new "deterrent" strategy in June 2020 that allowed for the use of nuclear weapons in response to a non-nuclear attack on Russia that threatened its existence.
On Tuesday, Russia's lower house of parliament, the State Duma, amended the law on military service, toughening the punishment for violation of military service duties -- such as desertion and evasion from service -- according to state news agency TASS.
The bill sets a jail term of up to 15 years for resistance related to military service or coercion to violate an official military order, involving violence or the threat of its use, during the period of mobilization or martial law.