Defence Secretary Ben Wallace lamented President Putin's recent actions and acknowledged the "worrying signs" coming from Ukraine.
Speaking about the crisis in Ukraine at a Joint Expeditionary Force defence ministerial meeting in Leicestershire, Mr Wallace addressed President Putin's declaration that he is going to recognise independent states in the Donbas region, including territory on the other side of the line of control.
The Defence Secretary said: "The very worrying sign is, of course, the clear fact that Russia has broken international law, and I just want to point correspondents to President Putin's speech itself."
Watch: European defence leaders meet in UK to discuss Russia-Ukraine crisis.
Images of heavy armour have prompted fears Russian tanks may already have crossed the border into Ukraine's streets.
Mr Wallace said: "We've seen, in open-source reporting, Russian military equipment moving into that region.
"We'll have to verify that, given what we know about Russian media performances and truth versus reality."