Russia on Thursday charged that calls for Syrian President Bashar al-Assad to step down are blocking efforts to end 16 months of unrest in the country.
Russian Foreign Minister Sergei Lavrov warned such calls -- made by the United States, several European and Arab governments and Turkey -- were fanning the flames of violence.
He also reiterated Moscow's claim that support for Syrian rebel groups was tantamount to backing terrorism.
"We propose things that would allow for an immediate ceasefire, but the other side says, 'No, either the regime capitulates or we will continue to back ... the opposition's armed fight', justifying terrorist acts," Lavrov said.
"As long as such support continues, what kind of humanitarian action can we talk about? -- including the initiatives of those who will not allow this fire to die down, but instead are fanning it," he told a joint briefing with Serbian Foreign Minister Vuk Jeremic in Moscow.
Moscow accused the United States on Wednesday of trying to justify terrorism against the Syrian government.
The claim raised tensions surrounding a diplomatic imbroglio in the UN Security Council, that has pitted Russia and China against their permanent veto-wielding counterparts, the United States, Britain and France.
Washington has said it will seek ways to tackle the crisis in Syria outside the world body.
Russia, an ally of Syria, has billions of dollars tied to Syrian president Bashar al-Assad's continued reign, and has vigorously defended Damascus from international pressure.
Moscow and Beijing, which is a principal consumer of Syrian exportable crude oil, have vetoed three motions by Western and Arab League nations in the security council aimed at pressuring Assad.
Meanwhile, rights groups say some 19,000 people - most of them civilians - have been slain since the popular uprising against Assad's rule erupted in March 2012.
Those numbers swell as forces loyal to Assad and rebels fight pitched battles in Syria's principal cities of Aleppo and Damascus.
A rebel push deep into the once-impregnable stronghold of Damascus was put down after weeks of bloody fighting in the capital when the government employed helicopter gunships and artillery in combination.
At present, overwhelming ground forces supported by some 100 tanks are being shifted to Syria's largest city and key economic center of Aleppo, which is home to some 2.5 million people.
Local activists say the government has already used warplanes, seen circling overhead, to strike rebel positions in the city. At least 24 were killed in clashes in Aleppo on Wednesday.
Rebel commanders in Aleppo province say thousands of fighters are streaming into the city to repel the impending government attack, expected over the weekend.
Aleppo sits near Syria's northern border with Turkey, making it a key strategic city for rebels who wish to bring supplies and fighters across the border.
Turkey, which reinforced its border with Syria following an incident in which Damascus shot down one of Ankara's warplanes, has given safe-haven to senior rebel commanders.