Russia said on Thursday that Syrian President Bashar al-Assad was losing control to rebels who may succeed in toppling his regime, dpa reported.
"The regime is losing more and more control in the country," Russian Deputy Minister of Foreign Affairs Mikhail Bogdanov told the Itar-Tass news agency. "We cannot rule out that the Syrian opposition can get a victory."
It was the first acknowledgement by Russia, which has vetoed UN Security Council resolutions condemning al-Assad, that its ally could be defeated in the civil war.
Bogdanov renewed Moscow's call for a compromise, saying it would take the opposition a long time to defeat the regime and the country would suffer more casualties.
Rebels have recently stepped up attacks on state institutions in the Damascus.
At least 17 people were Thursday killed in a car bombing apparently targeting a military facility near a school on the outskirts of Damascus, reported a activist group.
Seven children and two women were among the dead and at least 20 people were injured in the attack in the town of Katna, the Britain-based Syrian Observatory for Human Rights added.
The attack comes a day after at least nine people were killed in three explosions outside the Interior Ministry in Damascus.
Activists in Damascus said Interior Minister Mohammed al-Shaar was wounded in the attack, but his injuries were not life-threatening. The ministry said al-Shaar and his aides were safe.
It was the second attempt on al-Shaar's life. He had reportedly escaped death in July when a massive bombing in Damascus killed four top security officials, including the defence minister and al-Assad's brother-in-law.
Rebel attacks Thursday prompted authorities to tighten security around vital state institutions in Damascus, said activists.
"The battles are raging in the suburban areas of Daraya, Arbeen, Harasata," said Haytham al-Abdullah, a Syrian activist based in Damascus.
"Jets are using TNT barrel bombs to strike the opposition rebel bases in these areas," he told dpa.
US officials said Wednesday that al-Assad's government had begun using Scud missiles and barrel bombs against rebels.
News from Syria is hard to independently verify, as authorities have barred most foreign media from the country since a pro-democracy uprising started in March last year.
The US has officially invited leaders from the newly formed National Coalition of Syrian Opposition and Revolutionary Forces to visit Washington, a member of the bloc said.
"The invitation was extended when members of the coalition met with the US delegation on the sideline of the Friends of Syria conference held in Morocco on Wednesday," George Sabra, the head of the Syrian National Council, told dpa.
The United States has formally recognized the alliance earlier this week. Some 120 countries Wednesday endorsed the coalition, which was launched last month as a broad-based bloc against al-Assad's regime.