Putin announces partial mobilisation and threatens to use 'all means' available in Ukraine invasion

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

"If the territorial integrity of our country is threatened, we use all available means to protect our people - this is not a bluff," Putin said in a televised address to the nation.

Putin said he had signed a decree on a partial mobilisation, which significantly escalates the conflict.

Putin said his aim was to "liberate" east Ukraine's Donbas region, and that most people in the regions under Russian control did not want to be ruled by Kyiv. 

Russia's mobilisation was a predictable step that will prove extremely unpopular and underscores that the war is not going according to Moscow's plan, Ukrainian presidential adviser Mykhailo Podolyak said on Wednesday.

Podolyak said in a text message to Reuters that Putin was trying to shift the blame for starting an "unprovoked war" and Russia's worsening economic situation onto the West.

"Absolutely predictable appeal, which looks more like an attempt to justify their own failure," Podolyak wrote, giving the first reaction by Ukraine's presidential office.

Russia invaded Ukraine on February 24. The war has shifted dramatically in recent days as Kyiv rapidly reclaimed territory. 

In the apparently coordinated move, pro-Russian figures announced referendums for September 23-27 in Luhansk, Donetsk, Kherson and Zaporizhzhia provinces, representing around 15 percent of Ukrainian territory, or an area about the size of Hungary.

Some pro-Kremlin figures framed the referendums as an ultimatum to the West to accept Russian territorial gains or face an all-out war with a nuclear-armed foe.