MOSCOW - A high-level Russian diplomat conceded Thursday that Syrian rebels could oust President Bashar al-Assad, becoming the first top Kremlin official to say publicly that the government of Moscow's staunchest Middle East ally could collapse.

The comments of Deputy Foreign Minister Mikhail Bogdanov came as two more explosions rocked the suburbs of Damascus, the Syrian capital, the latest in a string of car bombings that appear to be part of an insurgent offensive on the city.

"We must face the facts: The possibility exists that the [Syrian] government may progressively lose control over an increasing part of the territory," Bogdanov told a Kremlin advisory body. "An opposition victory can't be excluded."

In Brussels, Anders Fogh Rasmussen, the NATO secretary-general, said that Assad's collapse was "only a question of time," a prediction now shared with much of the world, including Moscow.

But it was the blunt assessment from Russia - Assad's chief defender in the international arena - that seemed likely to add to the disquiet of a government already besieged by rebel forces and facing broad global condemnation.

Rejecting scenarios for a quick end to the conflict, the Russian diplomat painted a bleak picture of protracted combat and further mass casualties.

"The fighting will become even more intense, and [Syria] will lose tens of thousands, and perhaps hundreds of thousands, of civilians," Bogdanov said. "If such a price for the removal of the president seems acceptable to you, what can we do? We, of course, consider it absolutely unacceptable."

Adding to the sense of urgency, Kremlin officials confirmed that they were preparing for the evacuation of thousands of Russian citizens living in Syria, including many wives of Syrian men who studied in the eastern bloc during the Cold War era.

The Obama administration welcomed what it views as Russia's belated recognition of reality in Syria, and urged Moscow to help speed a transition in Damascus.

"We want to commend the Russian government for finally waking up to the reality and acknowledging that the regime's days are numbered," Victoria Nuland, a State Department spokeswoman, said in Washington. "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?"

Moscow has called for peace negotiations that do not exclude Assad, whose family has ruled Syria for more than 40 years. The armed opposition calls Assad a murderer who cannot be part of any peace talks and must go.

Russian officials were dismayed at this week's decision by the United States and more than 100 nations in the Friends of Syria group to designate an opposition coalition as the "legitimate representative" of the Syrian people.

The United States, said Russian Foreign Minister Sergei Lavrov this week, has "decided to place all bets" on an armed victory by the opposition, a viewpoint shared by many here.

The conflict is bearing down on Damascus, where heavy fighting has enveloped the city's outskirts and bombings have become a daily occurrence.

On Thursday, Syrian state media reported that car bombs had exploded in two suburban districts, killing 24 and wounding dozens, including many women and children.

A day earlier, state media reported that six bombs detonated in and around the capital, killing at least eight people. Three blasts went off near the Interior Ministry building, killing a parliament member and four others and injuring 23. But officials said the interior minister, the apparent target, survived with minor wounds.

Another bomb exploded Wednesday in a minibus in the capital's Mazzeh Jabal 86 neighborhood, state media said, killing three, including a journalist. The district, a frequent target of car bombings, is home to many security officials and adherents of Assad's minority Alawite sect, whose members generally support the government in the face of a rebellion led by members of the nation's Sunni Muslim majority.