Russian Foreign Minister Sergei Lavrov has said Western attempts to get Moscow to discuss sanctions against Syria contain “elements of blackmail”.
Mr Lavrov said the West had threatened to end a UN observer mission if Russia opposed its draft resolution.
Peace envoy Kofi Annan is due in Moscow, and is expected to urge Moscow to put more pressure on Syria’s leaders to begin a political transition.
Russia has strong ties with Syria and has vetoed foreign intervention calls.
It has circulated its own draft resolution calling for the extension of the observer mission’s mandate, which runs out this week. It does not contain any threat of sanctions against Damascus.
Mr Annan’s visit comes amid reports of some of the heaviest fighting in the conflict so far around Damascus.
The BBC’s Jim Muir says the clashes seem to be creeping ever closer to the heart of the capital and the centre of the regime’s power.
Activists and residents reported that tanks and mortars were used on the southern edge of the city, in areas like Tadhamon and Midan and around nearby Palestinian refugee camps.
Residents were said to be fleeing some areas, while in other parts of the city protesters blocked motorways with burning tyres.
Meanwhile the government has denied that it had used heavy weapons in its attack on the village of Tremseh on Thursday.
Activists initially described fighting in Tremseh, which is near the city of Hama, as a massacre of dozens of civilians, but later accounts suggested most of the dead were armed rebels.
UN observers at the scene have said Syrian forces used heavy artillery, tanks and helicopters, but Damascus has denied those allegations and says just two civilians had been killed.
The accusations, if proved, would mean Damascus had broken an agreement it made with Mr Annan.
Political transition
Mr Lavrov said said the West had told Russia to back a draft resolution on sanctions or it would “refuse to extend the mandate of the observer mission”.
It was “not right” to say that pressure should only be brought on the government of President Bashar al-Assad and not the opposition to end the conflict, he added.
“We do not support Assad,” he said. “We support what has been agreed by all sides.”
But he said it was unrealistic to expect Russia to persuade Mr Assad to step down.
“He will not leave power. And this is not because we are protecting him but because there is a very significant part of the Syrian population behind him,” he said.
Mr Annan is expected to meet Russian President Vladimir Putin and Foreign Minister Sergei Lavrov during two days of talks.
UN diplomats are attempting to find a way forward for the organisation’s monitoring mission in the country.
The mission’s mandate runs out on Friday, and Western nations are trying to get Russia and China to agree to a strengthened resolution authorising sanctions.
Mr Annan is expected to ask Mr Lavrov to put pressure on the Syrian authorities to begin a political transition.
The BBC’s Steve Rosenberg in Moscow says Mr Annan knows Russia’s role is crucial for the success of his peace initiative, but there is little sign that the Kremlin is ready to do what he says.
Part of the reason for this is that the Russians fear even greater chaos and bloodshed post-Assad, he says.
But Moscow is also deeply suspicious of the West and reluctant to endorse regime change, our correspondent adds, although this could change if it decides its own economic and geopolitical interests are better served by Mr Assad going.
UN Secretary General Ban Ki-moon is also expected to raise the Syrian issue with Chinese leaders when he arrives in Beijing for a China-Africa summit. China has joined Russia in vetoing several Western-backed UN draft resolutions calling for tougher action against the Syrian regime.
Meanwhile Morocco became the latest of many countries in the region and around the world to expel its Syrian ambassador.
The country’s foreign ministry said in a statement that Nabih Ismail had been declared persona non grata.
Some 16,000 people are thought to have been killed since the uprising against Mr Assad’s regime began in March 2011.