The UK's foreign secretary Philip Hammond has accused Vladimir Putin of acting like a "mid-20th century tyrant" over Ukraine.
Speaking to Sky News, Mr Hammond insisted Western sanctions were having an impact.
Mr Hammond said: "When coupled with the catastrophic effect on the Russian economy of the decline in the oil price they are putting pressure on the Kremlin.
"Putin is toughing this out but we all know in the end the economic facts cannot be ignored.
"If your economy is cratering you cannot support the kind of foreign adventures Putin is undertaking. He will have to trim his behaviour to reflect the decline in the Russian economy."
The Foreign Secretary branded Moscow's annexation of Crimea illegal and said it must be reversed.
He said: "This man has sent troops across an international border and occupied another country's territory in the 21st century acting like some mid-20th century tyrant. Civilised nations do not behave like that.
"We do not see any reason to tolerate this kind of outrageous and outdated behaviour from the Kremlin."
Peace talks
The comments come as Ukrainian President Petro Poroshenko has said he is optimistic peace talks with the leaders of Russia, France and Germany in Minsk on Wednesday would lead to a "swift and unconditional ceasefire".
A statement issued by his administration said progress had been made during a phone call between himself, Mr Putin, German Chancellor Angela Merkel and French President Francois Hollande.
Mrs Merkel and Mr Hollande are leading diplomatic efforts to halt the bloody conflict, which has claimed the lives of more than 5,000 people since April.
At the Munich Security Conference on Saturday, Mrs Merkel said the bid to end the fighting was "uncertain but worth trying", while Mr Hollande also warned it was "one of the last chances for peace".
And US Secretary of State John Kerry has insisted there is no split with Europe over handling the crisis.
US arms
US President Barack Obama is considering sending arms to the Ukraine government, which has been rejected by the German Chancellor, who argued it would not help the situation.
Mrs Merkel's opposition to arming Ukraine has led to a sharp rebuke from hawks in Washington, who have accused Berlin of turning its back on an ally.
Republican US Senator John McCain said: "The Ukrainians are being slaughtered and we're sending them blankets and meals. Blankets don't do well against Russian tanks."
NATO's top military commander has also said sending weapons should not be ruled out.
US Air Force General Philip Breedlove told reporters at the Munich conference: "I don't think we should preclude out of hand the possibility of the military option."
The Franco-German diplomatic push comes against an escalation in violence between the separatists and Ukrainian forces in the east of the country.
In the latest fighting, the Ukrainian military said the pro-Russian separatists had increased shelling of government forces and appeared to be amassing for new offensives on the key railway town of Debaltseve and the coastal city of Mariupol.
The US Vice President Joe Biden has backed the Franco-German peace bid - but made clear the White House stood ready to provide Ukraine with the means to defend itself.
He told the Munich summit: "Too many times President Putin has promised peace and delivered tanks, troops and weapons."
