Damascus: The death toll in Syrian protests rose as long-time Damascus ally Russia said President Bashar al-Assad had made "a lot of mistakes" in clamping down on the year-old demonstrations.

Fresh clashes broke out in the capital and security forces killed at least 30 people, all but two of them civilians, in violence elsewhere across the country, the Syrian Observatory for Human Rights said.

The capital's security clampdown follows what activists said was a hit-and-run attack in the heavily guarded Mazzeh neighbourhood on Monday that killed at least three rebels and a member of the security forces.

It also came on the heels of deadly twin suicide car bombings targeting security buildings in Damascus on Saturday.

The violence, however, is not all one-sided: Syria's armed opposition is kidnapping, torturing and executing security force members and government supporters, according to the New York-based Human Rights Watch.

"The Syrian government's brutal tactics cannot justify abuses by armed opposition groups," said Sarah Leah Whitson, HRW's Middle East director.

The rights watchdog group said the peaceful uprising had transformed into an armed insurgency, especially since early February, when the government attacked opposition strongholds throughout the country.

The Syrian National Council deplored the reported rights violations.

"We oppose any form of violence and support all the international conventions and treaties on the protection of human rights," the SNC said in a statement issued by spokeswoman Bassma Kodmani.

Russian Foreign Minister Sergei Lavrov said Assad acknowledged made "a lot of mistakes" since peaceful protests began in March 2011.

"We believe that the Syrian leadership responded incorrectly to the very first manifestations of the peaceful protests," he told Russia's Kommersant FM radio in a pre-recorded interview.

"The Syrian leadership -- despite the numerous promises it has made in response to our calls -- is making a lot of mistakes."

Russia has increasingly hinted it could drop its support for Assad after a year of violence that Syrian opposition activists say has claimed more than 9,100 lives.

Russia said it was ready to back either a UN Security Council statement or resolution on UN Arab League peace envoy Kofi Annan's proposal on ending the crisis as long as it contained no ultimatums.