In a pre-recorded announcement, Putin said the West “wants to destroy our country.”
Putin suggested that partial military mobilsation could involve conscription and that the decree had already been signed in a pre-recorded televised address.
He added that he had ordered an increase in funding to boost Russia’s weapons production.
Here’s everything you need to know.
What is partial military mobilsation?
A partial military mobilsation can mean a host of things, but increases the effort and resources available to a government during a conflict.
For example, such a move could enforce rules that require the Russian people or businesses need to contribute more to the war effort.
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.”
How many soldiers will be called up to fight in Ukraine?
A pre-recorded interview with Russia's minister of defence, Sergey Shoigu confirmed that the partial mobilisation will involve those who have military experience - and that 300,000 reservists will be mobilised.
The 300,000 is merely a fraction of the 25 million Russia has.
In an update he added that reservists won’t be taken all at once but according to need and that students would not be used and that they should remain ‘calm’ and ‘keep going to class’
Addressing the move in his speech Putin said: “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.
What did Putin say about the West and use of nuclear weapons?
Putin warned the West that Russia would use all the means at its disposal to protect its territory, saying: “It’s not a bluff.”
He accused the West in engaging in “nuclear blackmail” and noted “statements of some high-ranking representatives of the leading Nato states about the possibility of using nuclear weapons of mass destruction against Russia”.
He added: “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, and 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 may be ready to use nuclear weapons against western countries including Britain, a former adviser to Vladimir Putin has claimed.
Political scientist Sergei Markov was asked on BBC Radio 4’s Today programme if he believed the Russian leader had made a clear threat not just to use tactical nuclear weapons in Ukraine but also to start a general nuclear war that would kill everyone.
He replied “not everyone” but added it “could kill a lot of people in the western countries”.
Mr Markov said: “It was absolutely clear that Russia has no war against Ukraine. Russia has no reason to use technical nuclear weapons against Ukrainians. Ukrainians are our brothers but Ukrainians are occupied by western countries.
“It is western countries who are fighting against (the) Russian army using Ukrainian soldiers as their slaves.”
How has the West reacted to Putin’s speech?
Western nations have condemned Moscow's plans to hold urgent referendums in parts of Ukraine that are currently under Russian control.
The referendums will start on Friday in the Luhansk, Kherson and partly Russian-controlled Zaporizhzhia and Donetsk areas.
Defence Secretary Ben Wallace said: “President Putin’s breaking of his own promises to mobilise parts of his population and the illegal annexation of parts of Ukraine are an admission that his invasion is failing.
“He and his Defence Minister have sent tons of thousands of their own citizens to their death, ill equipped and badly let down.
"No amount of threats and propaganda can hide the fact that Ukraine is winning the war, the international community are united and Russia is becoming a pariah.”
In their latest intelligence brief, the Ministry of Defence stated that Russia’s military is facing significant pressures adding that "this is likely intended to limit the number of desertions and refusals and thereby to mitigate some of the immediate pressures.”
The UK's Foreign Office Minister Gillian Keegan has described Vladimir Putin's threat to the West that he has lots of weapons as "chilling", adding that the address was "more of Putin's lies"
She dubbed the address a “worrying escalation” adding : "It's a serious threat but it's one that's been made before.
"Some of the language there was quite concerning at the end and obviously we would urge for calm.
"It's something that we should take very seriously because, you know, we're not in control.
"I'm not sure he's in control either really. I mean, this is obviously an escalation and, of course, for the Russian people now they will be conscripted into this war."