Voting began on Friday in a Russian-controlled part of Ukraine in a referendum that Russia is expected to use to justify the annexation of four regions, with one Ukrainian official reported as saying voting was mandatory.

"Voting has started in the referendum on Zaporizhzhia region becoming a part of Russia as a constituent entity of the Russian Federation! We are coming home! Godspeed, friends!" said Vladimir Rogov, an official in the Russian-backed administration of that region.

The referendums have been widely condemned by the West as illegitimate and a precursor to illegal annexation.

Serhiy Gaidai, the Ukrainian governor of the Luhansk region, said that in the Russian-held town Bilovodsk, the head of one enterprise told employees the referendum was mandatory and those who refused to vote would be fired and their names given to the security service.

He said that in the town of Starobilsk, Russian authorities banned the population from leaving the city until Tuesday and armed groups had been sent to search homes and coerce people to get out to take part in the referendum.

Voting in the four regions of Luhansk, Donetsk, Kherson and Zaporizhzhia provinces, representing about 15% of Ukrainian territory, is due to run from Friday to Tuesday.

The votes come after Ukraine this month recaptured large swathes of territory in a counteroffensive, seven months after Russia invaded and launched a war that has killed thousands, displaced millions and damaged the global economy.

The referendums had been discussed for months by pro-Moscow authorities but Ukraine's recent victories prompted a scramble by officials to schedule them.

With Russian President Vladimir Putin also announcing this week a military draft to enlist 300,000 troops to fight in Ukraine, Moscow appears to be trying to regain the upper hand in the conflict.

Russia argues that it is an opportunity for people in the region to express their view.

"From the very start of the operation, we said that the peoples of the respective territories should decide their fate, and the whole current situation confirms that they want to be masters of their fate," Russian Foreign Minister Sergei Lavrov said this week.

Ukraine said Russia intends to frame the referendum results as a sign of popular support, and then use them as a pretext for annexation, similar to its takeover of Crimea in 2014, which the international community has not recognized.

Justifying Self-Defence

By incorporating the four areas into Russia, Moscow could justify military escalation as necessary to defend its territory. Putin on Wednesday said Russia would "use all the means at our disposal" to protect itself, an apparent reference to nuclear weapons. "This is not a bluff," he said.

"Encroachment onto Russian territory is a crime which allows you to use all the forces of self–defence," Dmitry Medvedev, who was Russia's president from 2008 to 2012, said in a post on Telegram.

Referendum results in favour of Russia are considered inevitable. The vote in Crimea in 2014, criticized internationally as rigged, had an official result of 97% in favour of formal annexation.

The referendums have been denounced by world leaders including US President Joe Biden, UN Secretary-General Antonio Guterres and French President Emmanuel Macron, as well as NATO, the European Union and the Organization for Security and Cooperation in Europe (OSCE).

The "sham referenda" are "illegal and illegitimate," NATO said.

The OSCE, which monitors elections, said the outcomes would have no legal force because they do not conform with Ukraine law or international standards and the areas are not secure.

There will be no independent observers, and much of the pre-war population has fled.

Russia already considers Luhansk and Donetsk, which together make up the Donbas region Moscow partially occupied in 2014, to be independent states.

Ukraine and the West consider all parts of Ukraine held by Russian forces to be illegally occupied. Russia does not fully control any of the four regions, with only around 60% of Donetsk region in Russian hands.

Ukraine has said the referendums were a sign Russia was running scared. "Any decision that the Russian leadership may take changes nothing for Ukraine," Ukraine President Volodymyr Zelenskiy said on Thursday.

"Of interest to us are strictly the tasks before us. This is the liberation of our country, defending our people and mobilizing world support (public opinion) to carry out those tasks," he added. 

Putin says Russia is carrying out a "special military operation" to demilitarize Ukraine, rid it of dangerous nationalists and defend Russia from NATO.

Kyiv and the West call Russia's actions an unprovoked, imperialist bid to reconquer a country that shook off Russian domination with the 1991 break-up of the Soviet Union.

'Losses'

Ukraine's General Staff said Russia had launched attacks in the Donetsk region and that Ukrainian shelling had wounded a Russian general in the Luhansk region.

"The enemy continues to suffer losses, in particular among the leadership," it said on Friday.

Russia has reportedly lost several high-ranking commanders during the seven-month war.

The head of Russian-backed separatists in Donetsk denounced Ukrainian attacks as "cynical barbarian shelling" intended to cause as much damage as possible to civilians.

"That is why we want to act quickly and with greater resolve with measures like the staging of the referendum," said Denis Pushilin.

Reuters is unable to verify battlefield reports.