Russia has said it hopes to avoid confrontation with the West
Seven of the world's leading industrialised nations have jointly condemned Russia's decision to recognise Georgia's breakaway regions.
Canada, France, Germany, Italy, Japan, the US and UK said Moscow's recognition of South Ossetia and Abkhazia violated Georgia's integrity and sovereignty.
Earlier, the UK's foreign secretary said Western countries should re-examine their relations with Russia.
David Miliband also warned Russia not to start a new Cold War.
Speaking during a visit to Ukraine, Mr Miliband said Moscow had not reconciled itself with the new map of the region and that the West should look at ways to reduce its dependence on Russian oil and gas.
Russia was, is and will continue to be the last country in the world that would want a repeat of the Cold War
French President Nicolas Sarkozy meanwhile described Russia's move to recognise South Ossetia and Abkhazia as an unacceptable attempt to change borders.
Russia said it was the last country that wanted a new Cold War.
Fighting between Russia and Georgia began on 7 August after the Georgian military tried to retake its Russian-backed breakaway province of South Ossetia by force.
Russian forces subsequently launched a counter-attack and the conflict ended with the ejection of Georgian troops from both South Ossetia and Abkhazia and an EU-brokered ceasefire.
In a statement, the Group of Seven said they condemned "the action of our fellow G8 member" and reasserted their support for the Georgian government.
"Russia's recognition of the independence of South Ossetia and Abkhazia violates the territorial integrity and sovereignty of Georgia and is contrary to UN Security Council Resolutions supported by Russia," the statement said.
The group also said it deplored Russia's "excessive use of military force in Georgia and its continued occupation of parts of Georgia".
"We call unanimously on the Russian government to implement in full the six-point peace plan brokered by President Sarkozy on behalf of the EU, in particular to withdraw its forces behind the pre-conflict lines," the statement added.
"We reassert our strong and continued support for Georgia's sovereignty within its internationally recognized borders and underline our respect and support for the democratic and legitimate government of Georgia as we pursue a peaceful, durable solution to this conflict."
The Russian government responded to earlier criticism from Western leaders by saying Moscow saw no threat of a new Cold War.
A spokesman for Prime Minister Vladimir Putin said Russia had been taking "measures of precaution" against Nato warships in the Black Sea, but hoped to avoid confrontation.
"I wouldn't agree that we really have a threat of a new Cold War. Russia was, is and will continue to be the last country in the world that would want a repeat of the Cold War," Dmitry Peskov said.
On Tuesday, Russian President Dmitry Medvedev said he had been obliged to recognise the independence of South Ossetia and Abkhazia following the "genocide" started by Georgian President Mikhail Saakashvili in South Ossetia in August.
He also blamed Georgia for failing to negotiate a peaceful settlement.
The Group of Seven's statement came only hours after Mr Miliband said the conflict between Russia and Georgia had "provided a rude awakening".
David Miliband said Russia must not start a new Cold War
In a speech to a group of students in Ukraine's capital, Kiev, Mr Miliband said Moscow's "unilateral attempt to redraw the map marks a moment of real significance".
Russian President, he said, had a "big responsibility not to start" a new Cold War.
Mr Miliband said the response of the EU and Nato to such "aggression" should be one of "hard-headed engagement".
"That means bolstering our allies, rebalancing the energy relationship with Russia, defending the rules of international institutions, and renewing efforts to tackle 'unresolved conflicts'," he explained.
Mr Miliband again rejected calls for Russia to be expelled from the G8, but did suggest the EU and Nato needed to review relations with it.
He also reiterated the British government's support for Ukraine's application for full Nato membership.
Ukraine's President, Victor Yushchenko, said it was a hostage in a war waged by Russia against states in the old Soviet bloc.
He told Mr Miliband that the brief conflict between Georgia and Russia earlier this month had exposed serious weaknesses in the powers of the UN and other international bodies.
Mr Yushchenko also called for Ukraine's defences to be strengthened and said his country would consider increasing the amount of money Russia pays for the lease of the port of Sevastopol, where it stations its Black Sea Fleet.
In other developments:
Georgia moved to reduce its diplomatic presence in Moscow, confirming its ambassador would not return
China addressed the crisis for the first time by expressing "concern" about developments in the region and urging dialogue. The comments came as Chinese President Hu Jintao met President Medvedev in Tajikistan ahead of a regional summit
German Chancellor Angela Merkel said the continued presence of Russian forces in Georgia proper was a grave ceasefire violation. She also agreed to send up to 15 military observers to Georgia as part of an expanded OSCE mission
Russian Foreign Minister Sergei Lavrov said Moscow would support the presence of more international monitors in the buffer zones