The Armed Forces minister has warned "tens of thousands of people could die" if Russia launches into an "extraordinarily stupid" conflict with Ukraine.
James Heappey said there is a "grave possibility" Russia may launch military action, with a hastily-arranged meeting between the US and Moscow this week in a bid to defuse tensions.
Mr Heappey said it is not "remotely realistic" British troops would engage in combat with Russia but added that Ukrainians are "ready to fight for every inch of their country".
He told Times Radio the UK had sent light anti-tank missiles to Ukraine in a show of support – with the Ministry of Defence (MOD) sharing photographs and videos online suggesting these had been received.
"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," he said.
"This is not something that people in Moscow should believe to be bloodless.
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"This is not something that the rest of the world should stand by and ignore."
Mr Heappey continued: "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."
This comes after the Prime Minister said the UK is doing "everything possible" to support the people of Ukraine in the face of a Russian "disinformation campaign".
Boris Johnson 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 said: "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.