Russian President Vladimir Putin announces a partial military mobilisation for Ukraine

President Vladimir Putin has ordered Russia's first military mobilisation since World War II, warning the West that if it continued what he called its "nuclear blackmail" that Moscow would respond with the might of all its vast arsenal.

In a televised address, Mr Putin said his aim was to "liberate" east Ukraine's Donbas region, and that most people in the region did not want to return to what he called the "yoke" of Ukraine.

He said he was defending Russian territories and that the West wanted to destroy the country. 

"We are talking about partial mobilisation, that is, only citizens who are currently in the reserve will be subject to conscription, and above all, those who served in the armed forces have a certain military specialty and relevant experience," Mr Putin said.

Russia's Defence Minister Sergei Shoigu said 300,000 reservists would be mobilised.

Mr Putin said the decision to partially mobilise was "fully adequate to the threats we face, namely to protect our homeland, its sovereignty and territorial integrity, to ensure the security of our people and people in the liberated territories".

Mr Putin accused Western leaders of engaging in nuclear blackmail, vowing to respond to any threats against Russia. 

"To those who allow themselves such statements regarding Russia, I want to remind you that our country also has various means of destruction, and for separate components and more modern than those of NATO countries," he said.

"When the territorial integrity of our country is threatened, to protect Russia and our people, we will certainly use all the means at our disposal."

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 now holds about 60 per cent of Donetsk and had captured nearly all of Luhansk by July after slow advances during months of intense fighting.

Those gains are now under threat after Russian forces were driven from neighbouring Kharkiv province this month, losing control of their main supply lines for much of the Donetsk and Luhansk front lines.

World will not allow Russia to use nuclear weapons

Ukrainian President Volodymyr Zelenskyy said on Wednesday he did not believe the world would allow Russia to use nuclear weapons and vowed to press on with liberating Ukrainian territory captured by Russian forces.

Mr Zelenskyy was speaking to Germany's BILD TV in an interview published hours after Mr Putin's announcement.

"Tomorrow Putin can say: apart from Ukraine, we also want a part of Poland, otherwise we will use nuclear weapons. We cannot make these compromises."

Mr Putin's mobilisation has come in response to Russia's failings on the battlefield, Mr Zelenskyy said.

"He sees that his units are simply running away," Mr Zelenskyy said, adding that Mr Putin "wants to drown Ukraine in blood, including the blood of his own soldiers".

Ukrainian presidential adviser Mykhailo Podolyak told Reuters that Russia's mobilisation was a predictable step that would prove extremely unpopular and underscore that the war was not going according to Moscow's plan.

Mr Podolyak said Mr Putin was trying to shift the blame for starting an "unprovoked war" and Russia's worsening economic situation onto the West.

Shortly after Mr Putin’s address, Russian media reported a sharp spike in demand for plane tickets abroad, even though far fewer of those have been available since the start of the war and they are much more expensive than before.

Putin's military mobilisation is proof 'his invasion is failing'

British Defence Secretary Ben Wallace described Mr Putin’s mobilisation announcement as "an admission that his invasion is failing".

"He and his defence minister have sent tens of thousands of their own citizens to their deaths, ill-equipped and badly led," Mr Wallace said in a statement.

"No amount of threats and propaganda can hide the fact that Ukraine is winning this war, the international community are united and Russia is becoming a global pariah."

Czech Prime Minister Petr Fiala said the mobilisation was "further proof that Russia is the sole aggressor".

US ambassador to Ukraine Bridget Brink said Russia had shown weakness by announcing the mobilisation of reserves and setting out the referenda in the Russian-occupied territories.

Lithuania raised the readiness level of its army's rapid response force "to prevent any provocations from the Russian side", Defence Minister Arvydas Anusauskas said on Wednesday.

A Department of Foreign Affairs and Trade spokesperson (DFAT) said Australia was "deeply concerned" by Mr Putin's military mobilisation and that Australia would continue to support the government and people of Ukraine. 

"President Putin's threats to use 'all means' at his disposal are an irresponsible escalation of rhetoric and his claims to be defending Russia's territorial integrity are untrue," the DFAT spokesperson said.

"Russia should immediately withdraw from Ukraine and cease its illegal and immoral aggression against the Ukrainian people."

In another signal that Russia is digging in for a protracted conflict, the Kremlin-controlled lower of house of parliament voted on Tuesday to toughen laws against desertion, surrender and looting by Russian troops.

Politicians also voted to introduce possible 10-year prison terms for soldiers refusing to fight.

If approved, as expected, by the upper house and then signed by Mr Putin, the legislation would strengthen commanders' hands against failing morale reported among soldiers.

Mr Putin's address to the nation comes a day after Russian-controlled regions in eastern and southern Ukraine announced plans to hold votes on becoming integral parts of Russia.

The referendums, which have been expected to take since the first months of the war, will start Friday in the Luhansk, Kherson and partly Russian-controlled Zaporizhzhia and Donetsk regions.

Mr Zelenskyy has brushed off those plans, saying they were a "sham" that would not be recognised by most countries.

AP/Reuters