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.

Russian police officers detain a person during an unsanctioned rally, after opposition activists called for street protests against the mobilisation of reservists ordered by President Vladimir Putin, in Moscow, Russia September 21, 2022.