Armed Forces minister James Heappey said there was a “grave possibility” that Russia may launch military action, as a hastily-arranged meeting between the US and Moscow is due this week in a bid to defuse tensions.
Mr Heappey said it was not “remotely realistic” that British troops would engage in combat with the Russian military, but he added the Ukrainians were “ready to fight for every inch of their country”.
Mr Heappey told Times Radio the UK had sent light anti-tank missiles to the country in a show of support.
Photographs and video shared online by the Ministry of Defence of Ukraine on Tuesday suggested these have been received.
But Mr Heappey warned: “What stands in front of us, what could be weeks away, is the first peer-on-peer, industrialised, digitised, top-tier army against top-tier army war that’s been on this continent for generations.
“Tens of thousands of people could die.
“This is not something that people in Moscow should believe to be bloodless. This is not something that the rest of the world should stand by and ignore.
“It’s right that all diplomatic avenues are being exhausted.
"I just hope that as we’re on the brink, people in Moscow start to reflect that thousands of people are going to die and that is not something that anybody should be remotely relaxed about.”
It comes after Boris Johnson said the UK is doing “everything possible” to support the people of Ukraine in the face of a Russian “disinformation campaign”.
The Prime Minister told the Cabinet that Russian president Vladimir Putin “must not be allowed to rewrite the rules” of international relations as tensions continue to mount. US Secretary of State Antony Blinken is set to meet his Russian counterpart in Switzerland on Friday in a bid to quell the hostilities.
A senior State Department official told reporters: “We are now at a point where Russia could launch an attack on Ukraine at any time.”
Reports have suggested Russia has massed 100,000 troops with tanks and other heavy weapons near the Ukrainian border in what many observers believe may be preparation for an invasion.
The Russian Embassy in the UK said the Government’s decision to supply “lethal weapons” to Ukraine would “fuel the crisis and increase tensions”.
UK defence secretary Ben Wallace told MPs on Monday the UK was supplying light anti-armour defensive weapons, with a “small number” of UK personnel travelling to the country to provide training.
The Prime Minister’s official spokesman said at the time: “There is a small infantry training team deploying to assist the Ukrainian armed forces to become familiar with the defensive systems we are providing and ensure they are able to use them as soon as possible.
“Operation Orbital, our training deployment in Ukraine, has a routine commitment of around 100 personnel – that will fluctuate depending on the type of training taking place.”