Why are parts of Ukraine holding referendums on joining Russia? Here's what you need to know

People in four occupied regions of southern and Eastern Ukraine will vote in the coming days on whether to become part of Russia, in referendums that Western governments and election experts described as a sham.

Separatists and Moscow-backed officials announced earlier this week that votes would be cast from Friday through Tuesday in four provinces: Luhansk, Donetsk, Kherson and Zaporizhzhia. They claim to have widespread public support for joining Russia.

The referendums coincide with Russian President Vladimir Putin announcing the mobilization of some 300,000 reservists and threatening nuclear retaliation for any attacks on Russian territory, amid battlefield setbacks against a Ukrainian counteroffensive.

Here's a look at what the referendums will entail and their potential implications:

Why are the referendums taking place?

Separatists who have controlled large chunks of the separatist Luhansk and Donetsk regions in Ukraine's Donbas since 2014 have long pushed for joining Russia and have shown little tolerance for dissent.

Earlier in summer, when the Kremlin hoped for a quick capture of all of the Donbas region, local officials talked about holding referendums in September, but amid the slow pace of Russia's offensive in the east, officials in Moscow talked about delaying the votes until November. The Kremlin's plans changed again after a lightning Ukrainian counteroffensive this month.

Experts see the referendums, which will take place with only a few days' notice, as a Russian propaganda tool to shore up public support at a time when its troops are struggling to maintain ground in Ukraine.

"[Russia] couldn't care less that we say that their referendums are a sham.... The [Russian] population is still largely buying into what's happening. That could change with this conscription," says Professor Robert Austin of the University of Toronto's Munk School of Global Affairs and Public Policy.

Annexing those regions would also give Russia an opportunity to claim self-defence and retaliate strongly against any Ukrainian counteroffensives there. Earlier this week, Putin threatened to use nuclear weapons to defend Russia's territory.

"They will say [it's self-defence], but no one in the world will believe that," said Borys Wrzesnewskyj, a former Canadian Liberal MP who heads the Ukrainian World Congress's Human Rights Commission.

Will the votes be legitimate?

The referendums are illegal under both international and Ukrainian law, including breaching the United Nations Charter.

"It is a means to acquire territory by force, and that is illegal," said Professor Marc Weller, who holds the Chair of International Law and International Constitutional Studies at the University of Cambridge in the U.K.

Observers expect the outcome of the votes will be predetermined by the Kremlin, with officials expected to announce that voters in each region overwhelmingly support joining Russia.

"The people on the ground are given their orders to deliver a certain percentage.... Whether it's 97 or 95 per cent, [Putin] is definitely going to tell whoever's implementing the referendum what result he's looking for," Austin said.

The referendums will take place without independent observers, and there is a lack of transparency over who will get to cast a ballot and under what conditions.

Former Canadian chief electoral officer Jean-Pierre Kingsley, who has previously led international observer missions for elections in Iraq, Haiti and other countries, said the referendum process lacks several key elements: an independent authority in charge, rules of conduct and enforcement of them, and sufficient time and information for voters to understand what the referendums are about.

"I wouldn't look for any of those things in the upcoming referendums, just like I didn't in Crimea," Kingsley said, referring to a hastily arranged 2014 vote in Ukraine's Crimea region over whether to join Russia.

Wrzesnewskyj described the vote as "literally a referendum under the gun."

"In a place that's been bombed, shelled, where your neighbours have have been killed, disappeared, tortured, and a so-called Russian occupation election official shows up with a soldier with a Kalashnikov and tells you to fill out a ballot and vote, how would you vote? You would vote to save your life."

People from those regions who were displaced, fighting on the front lines or forcibly transferred to Russian territory are unlikely to be involved in the vote.

Will Russia face consequences over referendums?

Many Western leaders, including Prime Minister Justin Trudeau and U.S. President Joe Biden, have denounced the referendums as a sham and said their countries would not recognize the outcomes.

However, it is not clear what further action they might take against Russia, given the enormity of sanctions already in place since the war began in February.

Ukrainian President Volodymyr Zelenskyy has called on the United Nations to strip Russia of its veto power at the UN Security Council.

In 2014, Russia was expelled from the G8 and sanctioned by many countries after sending troops into Crimea and holding a referendum where officials claimed 97 per cent of voters supported joining Russia.

Moscow used that vote as a justification to annex the Black Sea peninsula, in a move that was not recognized by most of the world. The vote was held under the close watch of Russian troops shortly after they had overtaken the region.

What's the current situation in areas holding votes?

Luhansk and Donetsk declared their independence from Ukraine weeks after Crimea's annexation, triggering eight years of fighting that eventually led Putin to launch an invasion in February, ostensibly to protect their residents.

Since then, Russian troops and local separatist forces have taken control of virtually all of the Luhansk region, but only about 60 per cent of Donetsk.

In the southern regions where referendums will be held, anti-Russian sentiment runs strong. Hundreds of pro-Kyiv activists have been arrested, with many alleging they were tortured. Others were forcibly deported, and tens of thousands fled.

How is this related to Putin's mobilization, nuclear threats?

A day after the referendums were announced, Putin ordered a partial mobilization of about 300,000 reservists to bolster his forces in Ukraine, and he also declared he was ready to use nuclear weapons to fend off any attacks on Russian territory.

Observers noted that Putin's decree is broad enough to allow the military to swell the numbers further if needed. Some reports suggest the Kremlin's goal is amassing one million men.

Dmitry Medvedev, deputy head of Russia's Security Council chaired by Putin, amplified the president's threat on Thursday, saying that after absorbing the four Ukrainian regions, Moscow could use "any Russian weapons, including strategic nuclear weapons," to defend them.