EU leaders are set to warn Russia their relations have reached a "crossroads" and that future ties will depend on it adhering to a ceasefire with Georgia.
They will also condemn Moscow's decision to recognise the independence of two breakaway regions of Georgia, according to a draft statement.
But there is no mention of sanctions against the EU's main energy supplier.
Earlier, Russia warned further Western support for Georgia's government would be a "historic" mistake.
Foreign Minister Sergei Lavrov also called for an embargo on arms supplies to Georgia until a different government was in place there.
The EU's foreign policy chief, Javier Solana, meanwhile said it was prepared to send hundreds of civilian monitors to Georgia to check if Russia was abiding by the EU-brokered ceasefire agreement.
Fighting between Russia and Georgia began on 7 August after the Georgian military tried to retake South Ossetia by force.
Russian forces launched a counter-attack and the conflict ended with the ejection of Georgian troops from South Ossetia and Abkhazia.
'Gravely concerned'
As leaders of the EU's 27 member states gathered in Brussels on Monday for an emergency summit on the crisis, sharp differences emerged between them on how to respond to the Russia's actions.
But the BBC's Oana Lungescu in Brussels says the draft conclusions of the meeting, which have been seen by the BBC, are tougher than many expected.
"The European Council is gravely concerned by the open conflict which has broken out in Georgia, by the resulting violence and by the disproportionate reaction of Russia," the draft says.
It also calls for the appointment of an EU special representative and the despatch of a mission to the region to review of the implementation of the ceasefire deal.
"In the light of the situation and in particular the implementation by Russia of all its commitments under the six-point [ceasefire] plan, [the review] may lead to decisions on the continuation of discussions on the future of relations between the Union and Russia in various areas," it adds.
Although there is no mention of sanctions against Russia, the draft says relations with Russia have "reached a crossroads" and warns the EU will remain "vigilant".
"We are convinced that it is in Russia's own interest not to isolate itself from Europe. We expect Russia to behave in a responsible manner, honouring all its commitments," it says.
There will also be a strong signal of support for Georgia, with support for a donors' conference for reconstruction, the promise of a free trade area and fewer travel restrictions on its citizens.
Ahead of the summit, UK Prime Minister Gordon Brown urged the EU to suspend talks on a long-delayed partnership agreement with Russia.
But France, which currently holds the EU presidency and brokered the ceasefire agreement between Russia and Georgia last month, said Europe did not want to "recreate the Cold War".
"By pointing the finger at Russia, we isolate it and continue to trample on it," Prime Minister Francois Fillon said. "This is not the way France has chosen. It's not the way Europe has chosen... and the word 'sanctions' is not on the agenda."
German Chancellor Angela Merkel also said the EU should not break off dialogue with Moscow but instead "speak clearly", echoing earlier comments by Foreign Minister Frank-Walter Steinmeier.
Georgians are holding rallies in Tbilisi and in other European capitals to coincide with the Brussels summit.
President Mikhail Saakashvili told a crowd of thousands in Tbilisi's Freedom Square that Georgia was "united as never before" and urged EU leaders not to give up in the face of Russian "aggression".
"Today we can say that Georgia is not alone, because the whole world is standing beside us," he said. "Georgia will never stop resisting, Georgia will never surrender."
'Responsible state'
Earlier, Russia's Foreign Minister Sergei Lavrov warned the US and its allies that supporting President Saakashvili would be a historic mistake, and called for an arms embargo "while a different government turns Georgia into a normal state".
"To protect the region from the recurrence of violence, Russia will continue taking measures to punish the guilty, so that this regime is never able to do evil," he said.
Speaking in Moscow, Mr Lavrov said Russia had returned to the world stage as a responsible state which could defend its citizens.
Mr Lavrov's comments follow Mr Medvedev's redefining of Russia's foreign policy principles.
Russia, the Kremlin leader declared, would no longer accept a situation whereby a single country, like the US, sought global domination.
Mr Medvedev also pledged to defend the lives and dignity of Russian citizens, wherever they are located.
He made it clear that there were parts of the world where Russia sees itself as having privileged interests.
Russia's conflict with Georgia began on 7 August when Georgia tried to regain control of South Ossetia by force, and Russia counter-attacked deep into Georgia.
(BBC)
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