The Ukranian military intelligence services are predicting that Russia will invade as soon as early next year.
US officials reportedly told the EU earlier this month that Russia could be planning an invasion, following the months-long build up of troops and military equipment on the Ukraine border.
Comments made by a Kremlin-linked foreign policy analyst on Wednesday (24 November) suggest that Russia could launch an attack on Ukraine if the country is allowed to join Nato.
What is happening in Ukraine?
Intelligence sources say that Russian is increasing its military personnel on the border of Ukraine, potentially in preparation for an invasion.
There have been reports previously this year that the Kremlin was moving troops and equipment in the region, although US sources say the mobilisations this time are of a different scale.
Around 90,000 troops are thought to be in position near the border, following new deployments to Crimea and the arrival of the First Tank Army to Voronezh.
Since mid-March analysts and the Ukranian government have reported a build-up of Russian troops on its borders, including tanks and artillery units.
Previous reports suggested that as many as 80,000 units were stationed in Crimea and near the eastern border area of Ukraine at the height of tensions back in April.
A call between US president Joe Biden and his Russian counterpart seemed to resolve the tensions at the time, although recent developments have been met with concern.
Putin has continually insisted that the buildup of troops is either part of planned exercises or in response to Nato forces operating nearby.
Putin has claimed that he told his own military not to conduct unplanned drills, because “there’s no need to aggravate the situation further”.
He added: “You get the impression they just won’t let us let our guard down. Well, let them know that we’re not letting our guard down.
Tensions are now reaching the highest points since Russia invaded Ukraine in 2014, with fighting still ongoing in the Donbas region of the country as a result of that earlier conflict.
After a pro-Western revolution in the country in 2014, Russia invaded and annexed part of the country, Crimea, while fuelling a conflict in the Donbas region by backing separatist forces.
After being warned of the threat posed by Russia, EU leaders are ‘watching the situation very closely”, according to EU spokesperson Peter Stano.
In a statement, he said, “the information we gathered so far is rather worrying,” and the EU has been “looking into ways to enhance Ukraine’s resilience in case of further escalation”.
Speaking on Thursday (25 November) outgoing German Chancellor Angela Merkel said the EU must be prepared to respond to acts of “aggression” toward the Ukraine.
Addressing a press conference in Berlin, Merkel said: "Any further aggression against the sovereignty of Ukraine would carry a high price.”
Will this lead to war with Russia?
The UK has recently agreed a deal with Ukraine to enable to country to access loans to purchase military equipment to boost its navy.
Defence Secretary Ben Wallace signed off on the new agreement last week, which could be seen as a provocation by Russia.
Ukraine is not a NATO member state, but member states have pledged to side with the country against Russia should the latter provoke a new conflict.
The outgoing head of the UK’s armed forces, Gen Sir Nick Carter, has said that the UK must be prepared for conflict, although he doubts the Kremlin wants a ‘hot war’.
Speaking to Sky News earlier this month, Carter said: “Russia probably regards the global strategic context as a continuous struggle in which, I think, they would apply all the instruments of national power to achieve their objectives. But in so doing, [the Russians] don’t want to bring on a hot war.
Carter referred to comments made by former MI6 officer Christopher Steele, who said Moscow believes it is at war with the West.
He said: “So, yes, in a way I think he’s right. The question, of course, is how you define war and I, as a soldier, would tend to define war as the actual act of combat and fighting, and I don’t think they want that.
“I think they want to try and achieve their objective in rather more nuanced ways.”
He also described how Russia may be using indirect tactics, such as orchestrating the movement of refugees into the EU via its ally Belarus, to provoke tensions.
Speaking to BBC One’s Andrew Marr he later said Russia was in a “hybrid playbook where you link disinformation to destabilisation and the idea of pushing migrants on to the European Union’s borders is a classic example of that sort of thing”.
The military chief said he didn’t know if the rising tensions would lead to direct conflict. He said: “I think we have to be on our guard and make sure deterrence prevails and critically we have to make sure there is unity in the Nato alliance and we don’t allow any gaps to occur in our collective position.”
The Mirror has reported that a small deployment of SAS and other military units from the UK are on standby ready to be sent to the region if tensions flare.
A source told the paper: “The high readiness element of the brigade was told it may need to deploy at very short notice.
“Between 400 and 600 troops are ready. Their equipment is packed and they are ready to fly to Ukraine and either land or parachute in. They have trained for both eventualities.”