The statement by Russia's deputy foreign minister comes as rebels make gains across the country and on the international stage and one day after the U.S. and NATO said Assad's forces had fired Scud missiles at rebel areas.
Rebels have seized large swaths of territory in north Syria and appear to be expanding their control outside of Damascus, pushing the fight closer to the seat of Assad's power. On Wednesday, the U.S., Europe and their allies recognized the newly reorganized opposition leadership, giving it a stamp of credibility and possibly paving the way for greater international aid to those fighting Assad's forces.
World powers have remained deadlocked on how to end Syria's crisis, with the U.S. Europe and many Arab nations calling on Assad to stand down while Russia, China and Iran continue to back him.
But Russian Deputy Foreign Minister Mikhail Bogdanov offered the first acknowledgement yet from a top Russian official that Assad's regime may be in trouble.
"We must look at the facts: There is a trend for the government to progressively lose control over an increasing part of the territory," Bogdanov said during hearings at the Kremlin advisory body, the Public Chamber. "The opposition victory can't be excluded."
He didn't suggest that Russia would immediately change its stance toward Assad and called for a political solution, saying continued war would be tragic.
"The fighting will become even more intense, and you will lose tens of thousands and, perhaps, hundreds of thousands of people," he said. "If such a price for the ouster of the president seems acceptable to you, what can we do? We, of course, consider it absolutely unacceptable."
The bomb blast in the Damascus suburb of Qatana, southwest of the capital, is the latest in a string of similar bombings in and around Damascus that the government says have killed at least 25 people in the last two days.
The government blames the bombings on terrorists, the term it uses to refer to rebel fighters.
While no one has claimed responsibility for the bombings, some have targeted government buildings and killed officials, suggesting that rebels who don't have the firepower to engage Assad's forces in the capital are resorting to other measures to weaken his regime.
Thursday's attack, however, killed civilians and could add to a growing wariness of the rebels among many Syrians.
Syria's SANA news agency said a car packed with explosives blew up near a school in a residential part of Qatana. The report quoted medics from a nearby hospital as saying 16 people were killed, including seven children and "a number" of women. It said nearly two dozen people were wounded.
The Britain-based Syrian Observatory for Human Rights said the blast killed 17 people, including seven children and two women, adding that it was near a military residence. It did not say who carried out the attack.
Similar attacks hit four places in and around Damascus on Wednesday. Three bombs collapsed walls of the Interior Ministry building, killing at least five people. One of the dead was Syrian parliament member Abdullah Qairouz, SANA reported.
Other explosions Wednesday hit near the Palace of Justice, in the suburb of Jermana and in the upscale Mezzeh 86 district, heavily populated by members of Assad's minority Alawite sect. One of the three killed in that that bombing was a state TV journalist named Anmar Mohammed, SANA said.
The Observatory also reported the deaths of Qairouz and Mohammed and said the number of those killed in the Interior Ministry bombing had risen to nine.
Opposition activists suggested that the bombings were part of a new strategy by rebels to weaken Assad control of the capital by chipping away at his security forces with guerrilla style operations
"The Free Army is targeting military areas and security offices to try to lessen the number of forces that Assad has in the city," an activist named Ahmed said via Skype. He gave only his first name for fear of retribution.
Assigning responsibility for the blasts, however, remains difficult because rebels tend to blame attacks that kill civilians on the regime without providing evidence while competing groups often claim successful operations.
Assad's forces, too, appear to be escalating the fight. On Wednesday, two U.S. officials said the army had fired scud missiles from Damascus into northern Syria. The officials spoke on condition of anonymity because they weren't authorized to discuss the matter.
One official estimated the army fired more than a half dozen Scuds.
In Brussels, a NATO official confirmed that the alliance's intelligence indicates the firing of Scud-type missiles.
Anti-regime activists say more than 40,000 people have been killed since the start of the anti-Assad uprising in March 2011.