Russian President Vladimir Putin is behaving like a "mid-20th century tyrant", British Foreign Secretary Philip Hammond said on Sunday, urging him to change track and save Russia's economy from further decline.
He told Sky News television that supplying arms from Britain to Ukraine would not be the right thing to do "at the moment", but insisted London's position would be kept under review.
"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," Hammond said of Putin.
"Civilised nations do not behave like that in the 21st century. We live in a rules-based society. We want the Russian people to be part of that international community.
"We want Russia to enjoy the kind of economic growth and rising standards of living that people in the rest of Europe enjoy and we do not see any reason to tolerate this kind of outrageous and outdated behaviour from the Kremlin."
French, German and Ukrainian leaders are planning a summit with Putin for Wednesday in a frantic bid to halt the escalating bloodshed in east Ukraine.
The four leaders talked by phone on Sunday as part of urgent efforts to achieve a "comprehensive settlement" in the 10-month conflict between Ukrainian forces and pro-Russian rebels, Berlin said.
Hammond said Britain was not involved in the discussions as it was not practical to have a "committee of 10" talking to Moscow.
He said the international talks were "one of the last opportunities that Russia will have to avoid yet further significant damage to its economy which is bound to happen if the intransigence of Vladimir Putin forces the rest of the world to increase and tighten the sanctions from which Russia's economy is already reeling."
Putin "will have to trim his behaviour to reflect the decline in the Russian economy."
Biden asks Putin to "get out of Ukraine"
Meanwhile, US Vice President Joe Biden has asked Russian President Vladimir Putin simply to "get out of Ukraine."
Speaking at the Munich Security Conference in Germany, Biden said the conflict in Ukraine had moved beyond the need for a "reset" with the relationship, instead requiring a "re-assertion" of the "fundamental bedrock principles on which European freedom and stability rest."
Biden's blunt comments come at a time of increasing violence in Ukraine, with at least 224 killed and more than 540 injured in the final three weeks of January, according to the UN High Commissioner for Human Rights.
(With PTI inputs)