STORY: Russian President Vladimir Putin called up reservists to fight in Ukraine on Wednesday, signifying a major escalation in the war.

Speaking in a rare, televized address, Putin said Moscow would respond with the might of all its vast arsenal if the West pursued what he called its "nuclear blackmail" over the conflict.

“If the territorial integrity of our country is threatened, we will without question use all the means at our disposal to protect Russia and our people. This is not a bluff."

It is Russia’s first such mobilization since World War II.

Russia's defense minister Sergei Shoigu said the partial mobilization - which begins immediately - would see 300,000 reservists called up.

Adding that it would apply to those with previous military experience.

In his address, Putin said the partial mobilization of 2 million-strong military reservists was to defend Russia and its territories - and that the West did not want peace in Ukraine.

Ukrainian President Volodymyr Zelenskiy said he did not believe the world would allow Putin to use nuclear weapons.

Speaking to Germany’s BILD TV on Wednesday, he vowed to press on with liberating Ukrainian territory captured by the Russians.

In Moscow, some men expressed concerns over Putin's draft.

“You always feel worried in moments like these. Because if you have a wife and kids and you think about it. I would not want to leave them in case something happens”.

The mobilization call comes after recent setbacks for Moscow’s forces.

A Ukrainian counter offensive has driven them from areas they had captured in northeast Ukraine and they are bogged down in the south.

The move has been condemned by Western leaders, with Germany’s vice chancellor describing it as “an escalation.”

China’s foreign ministry urged all parties to engage in dialogue.

Ukrainians, however, remained defiant.

"The threat would be bigger if there was general mobilization, but I think at this point, Putin is afraid to take such a step because Russians would rather fight with words ”

“Putin doesn't know what to do so now he tries to make people fear his words. This is my opinion.”

Speaking to Reuters, Ukrainian presidential adviser Mykhailo Podolyak said the Russian mobilization was a predictable step that would prove extremely unpopular.

He added it underscored that the war was not going according to Moscow's plan.