Moscow acknowledged that the Syrian regime, its longtime ally, might lose its battle with Arab- and Western-backed rebels, 21 months into a conflict that has cost tens of thousands of lives.
The United States welcomed the apparent shift in Russia's stand, saying it appeared Moscow was "finally waking up to the reality" that the regime was on its way out.
The Russian comments came a day after Syria's interior minister was lightly wounded in a bold Damascus attack and claims, denied by the government, that an increasingly desperate regime had begun using Scud missiles against its foes.
Jihadists who have been at the forefront of latest rebel advances claimed the deadly Wednesday attack on the interior ministry.
And car bomb attacks on Thursday at an army residential block southwest of Damascus killed 24 people, state media said, further highlighting the regime's vulnerability even around the capital.
Russia's Deputy Foreign Minister Mikhail Bogdanov's said Arab and Western recognition of the opposition as the sole legitimate representative of the Syrian people had emboldened rebels to press their military campaign rather than seek the negotiated solution championed by Moscow.
"They (the rebels) are saying that victory is not far away, 'let's take Aleppo, let's take Damascus,'" the RIA Novosti news agency quoted him as saying.
"The recognition of the opposition, the training with rebel fighters and the weapons from abroad are now only inspiring the opposition."
In recent weeks, rebel capture of a series of key army bases, notably by jihadists, has given them control of large swathes of northern and eastern Syria, and Bogdanov said military defeat for Assad's regime could no longer be ruled out.
"As for preparing for victory by the opposition, this, of course, cannot be excluded," Russia's ITAR-TASS news agency quoted him as saying.
"You need to look the facts in the eyes -- the government regime is losing more and more control over a large part of the country's territory."
Those views were echoed by NATO chief Anders Fogh Rasmussen.
"I think the regime in Damascus is approaching collapse... it is only a question of time," Rasmussen said in Brussels.
In Washington, State Department spokeswoman Victoria Nuland said: "We want to commend the Russian government for finally waking up to the reality and acknowledging that the regime's days are numbered.
"I think the question now is, will the Russian government join those of us in the international community who are working with the opposition to try to have a smooth democratic transition?"
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A car bombing on Thursday in the government-held town of Qatana, southwest of Damascus, struck near an elementary school. Seven children were among the 16 dead and many of the 23 wounded, state media and the Syrian Observatory for Human Rights said.
Separately, eight civilians, mostly women and children, were killed by a car bomb in the town of Jdaidet Artuz, state television reported.
At least 98 people, including 74 civilians, were killed across Syria on Thursday, said the Observatory, which relies on activists and medics for its information.
On Wednesday, a bombing of the interior ministry killed at least five people and put Interior Minister Mohammed Ibrahim al-Shaar in hospital with a shoulder injury sustained when his office ceiling collapsed, a security source told AFP.
The jihadist Al-Nusra Front claimed that two of its men were responsible for the attack.
"Thank God, we targeted the interior ministry building in Kfar Sousa district in Damascus at 5:30 pm on Wednesday, December 12," the extremist group Tweeted on Thursday.
The security source said a traitor inside the ministry's own protection service had made possible the attack.
"It is impossible to get near the ministry gate except in an official vehicle," the source said.
Shaar narrowly escaped death in a spectacular July 18 bombing that claimed the lives of four other top security officials, including the defence minister and Assad's brother-in-law.
The military on Thursday launched air strikes against rebel positions along the Damascus airport road, which was briefly closed by rebel fire late last month, and in the town of Daraya southwest of the capital, the Britain-based Observatory said.
Meanwhile, a US official said the regime had used powerful, unguided Scud missiles on Monday to target rebels in zones now beyond the range of artillery. That was corroborated by a former Syrian officer who served in a surface-to-surface missile battalion and by a soldier who defected on Tuesday.
The Syrian foreign ministry on Thursday categorically denied those claims, calling them "biased and conspiratorial rumours."
"It is known that Scuds are strategic, long-range missiles and are not suited for use against armed terrorist gangs," it said.
The unguided Scud can deliver a payload of 3,500 kilos (7,700 pounds) or more over a range of 200 kilometres (125 miles) or more, defence analysts say.
In other developments, Amnesty International said the National Coalition of Syrian opposition forces that has won widespread recognition must work to free Ukrainian journalist Ankhar Kotchneva, who was kidnapped two months ago.
The release of Kotchneva must be the "first test" of the opposition coalition, a statement said.