Moscow replaced its top logistics general on Saturday after a series of setbacks when the Kremlin-held regions of eastern and southern Ukraine voted to belong to Russia for a second day.

The changing of the guard comes amid a major mobilization campaign by Russia after the invasion of Ukraine revealed widespread logistical difficulties, with Kyiv now reclaiming more and more territory.

Russia’s invasion and the Ukrainian army’s recent successes in a lightning-fast counteroffensive have exposed key logistical flaws, with some analysts seeing logistics as the weak link in the Moscow army.

“Army General Dmitry Bulgakov has been relieved of the post of deputy defense minister” and will be replaced by 60-year-old Colonel-General Mikhail Mizintsev, the defense ministry said.

Russia’s partial mobilization announced on Wednesday will likely be one of its first major logistical challenges, as hundreds of thousands of reservists that are called up need to be equipped and trained before deployment.

The vote on whether Russia should annex four regions of Ukraine began on Friday, dramatically raising the stakes seven months after Moscow troops invaded.

US President Joe Biden has dismissed the referendums as “a sham… a false pretext to try to forcibly annex parts of Ukraine in flagrant violation of international law”.

Even Beijing, Moscow’s closest ally since the war began in February, reacted.

Chinese Foreign Minister Wang Yi – in a statement to his Ukrainian counterpart Dmytro Kuleba at the UN General Assembly on Friday – said the “sovereignty and territorial integrity of all countries must be respected”.

Voting will take place in the Russian-controlled regions of Donetsk and Lugansk to the east, and Kherson and Zaporizhia to the south.

For four days, the authorities go door to door for four days to collect votes. Polling stations then open on Tuesday for residents to cast ballots on the final day. Results are expected as early as late Tuesday or Wednesday.

“Ultimately, things are moving in the direction of restoring the Soviet Union. The referendum is a step in that direction,” Leonid, a 59-year-old military official, told AFP.

The integration of the four regions into Russia would represent a major escalation of the conflict, as Moscow would view any military move there as an attack on its own territory.

Ukrainian forces said they would retake territory from Moscow-backed separatists in the very countries Russia wants to assimilate.

The quick referendums were only announced this week after a Ukrainian counter-offensive seized most of the northeastern region of Kharkiv – and brought hundreds of settlements back under Kiev’s control after months of Russian occupation.

Irpin, near the capital, has been retaken after weeks of fighting and residents have gathered to start rebuilding before winter sets in.

More than 100 apartment blocks in Irpin – dubbed a “hero city” by President Volodymyr Zelenskyy for holding back Russian invaders – were badly damaged by shelling.

The head of his building’s residents’ association, Mykhailo Kyrylenko, proudly looked at the new roof that was taking shape.

“People don’t have much money, but they have agreed” to donate funds to gradually restore the destroyed houses, he told AFP news agency.

Putin warned this week that Moscow will use “all means” to protect its territory – what former Russian leader Dmitry Medvedev said on social media could include the use of “strategic nuclear weapons”.

The referendum commemorates the referendum following Russia’s annexation of Ukraine’s Crimea in 2014.

Ukrainian President Volodymyr Zelenskyy denounced the elections, calling them “a crime against international and Ukrainian law” on Friday.

The G7 states said the elections will “never” be recognized and will have “no legal effect or legitimacy”.

Elsewhere, UN investigators on Friday accused Russia of committing war crimes on a “massive scale” in Ukraine — including bombings, executions, torture and appalling sexual violence.

Erik Mose of the Commission of Inquiry – an investigative team set up by the Security Council in March – said they had seen evidence of a “large number of executions” and the rape and torture of children.

In the eastern Kharkiv region, Ukrainian officials said on Friday they had completed the exhumation of 447 bodies from a site near the town of Izyum, which was retaken by Russian forces.

“Most of them show signs of violent death, and 30 show signs of torture,” Kharkiv regional governor Oleg Synegubov said.

“There are corpses with ropes around their necks, with their hands tied, with broken limbs and gunshot wounds.”

The Kremlin accuses Kyiv of fabricating evidence of the alleged war crimes.