As Vladimir Putin warns he is willing to use any military means necessary in the war with Ukraine, experts say the possibility of Russia using nuclear weapons must be taken seriously.
In a televised address this week the Russian leader ordered a partial military mobilisation — the country's first since World War II — warning that if the West continued what he called its "nuclear blackmail", Moscow would respond with its full military arsenal.
"If the territorial integrity of our country is threatened, we use all available means to protect our people — this is not a bluff," Mr Putin said.
Retired US Army major John Spencer told ABC News Daily he believed Mr Putin was willing to use nuclear weapons.
"I personally think that it's a credible threat", he said.
"[Russia] has the second largest arsenal of nuclear weapons in the world, only behind the United States."
"He's a terrorist with nuclear weapons, I really can't put it any other way."
But Mr Spencer, who is the chair of urban warfare at the Modern War Institute, said the use of such weapons would ultimately be counter-productive for Russia.
"If a nuclear, biological, chemical weapon is used in Ukraine — even if it's a tactical one — it won't lead to Russia achieving their strategic goals of overtaking Ukraine," he said.
"It will only cause the war to change because other nations will have to respond based on what is used."
Mr Spencer added that the use of weapons of mass destruction (WMD) would change the rules on which the war is being fought, opening up the likelihood of retaliatory strikes by the West.
"In my opinion, if Russia uses a WMD, that is the end of the Putin regime and the end of the Russian Federation as it exists today," he said.
Russian military analyst Pavel Felgenhauer is also sceptical about whether nuclear weapons would further Russia's aims.
Speaking to RN Breakfast, Dr Felgenhauer said their use would contradict Vladimir Putin's whole rationale for the invasion.
"Putin said that Ukrainians are basically like Russians that have been taken over by bad guys," he said.
"Hitting cities that they consider historically to be the heartland of Russia with nukes and flattening them, that doesn't make much sense."
"I don't believe that nuclear usage right now is imminent and that's more or less what the response has been from Washington, that they take it seriously, but they don't believe that it's coming any time soon."
How many troops could Russia mobilise?
In announcing a partial military mobilisation, Russia's Defence Minister Sergei Shoigu signalled that as many as 300,000 Russian reservists could be deployed to Ukraine.
But John Spencer said the Russian reservists were poorly skilled and would take considerable time to be mobilised.
"Russia doesn't have a reserve force," he said.
"He's basically saying that people who have served in the military at some point are being forced back into the military and will get two weeks of training and then be sent to the front lines in Ukraine."
"The first round will probably be more like 10,000 to 20,000 troops — not 300,000 — because [Putin] just doesn't have the infrastructure to do that."
Mr Spencer said the move is a desperate attempt by the Kremlin to replenish an army that's suffered significant losses in recent weeks.
"They've lost, by some estimates, over 80,000 soldiers," he said.
"Ukraine is destroying their military, so he wants to take these men who served at some point in the military and then rush them to fill the gaps … to hold the Donbas [region]."
The referendum strategy
At the same time as Russia was attempting to mobilise more troops, John Spencer pointed to another strategy he said the Kremlin was deploying in the east of Ukraine: referendums.
In the past few days, four Russian-controlled regions — Luhansk, Donetsk, Kherson and Zaporizhzhia — all declared they would hold referendums on joining Russia.
Russia does not fully control any of the four regions, with only around 60 per cent of the Donetsk region in Russian hands, and a small part of the Luhansk region recently recaptured by Ukrainian forces.
Ukraine's Foreign Minister Dmytro Kuleba has called the votes "sham referendums", saying they wouldn't change anything.
But Mr Spencer said Russia was planning to use the referendums as part of its military strategy.
"They'll hold these votes to say that all these people in these territories voted that they want to be Russian," he said.
"Russia will claim 'this is Russian land', signing it into their constitution so they can make up this narrative that they're defending Russian territory."
"Then they'll put in Russian proxies to be the government and basically subjugate the people of these areas."
Russia's Foreign Minister Sergei Lavrov said this week it was up to the people living in separatist-controlled areas of Ukraine to decide if they wanted to hold referendums on joining Russia.
"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," he said.
Dr Pavel Felgenhauer said the referendums — which are expected to take place between September 23 and September 27 — would be used as further justification for the military mobilisation.
"It means that it would be Russian territory, occupied by Ukrainians, supported by the West, and that Russia has to liberate them," he said.
"This changes the nature of the war as Russia is fighting (as Putin claimed in his speech) for its territory and existence."
Can Ukraine still win the war?
Despite the mobilisation of more Russian troops and the escalation in language, John Spencer believes Ukraine will still ultimately win the war.
"I don't think that changes what I predict will ultimately be a Ukrainian victory," he said.
"Rushing literally prisoners to the front … would not turn the tide of the war in their favour."
"[Putin's] lost so much momentum, his equipment is so badly maintained, but most importantly … if a soldier doesn't have the will to fight, they literally won't shoot back."
Dr Felgenhauer said the prospect of an ongoing war could also be politically dangerous for Vladimir Putin domestically.
"If the Russian forces continue to falter on the battlefield in the coming months, then we're talking about a winter campaign then again spring, then maybe a summer campaign into 2023," he said.
"If it continues and things don't get better significantly, then the Putin regime could be in serious problems."
