Air raid blasts which hit Damascus Monday, heard coming from several outlying districts, rattled windows in the city centre and were among the most intense in Damascus since the beginning of Syria's 19-month conflict, an AFP correspondent said.

They were followed by two car bombings in and around the capital.

The first struck the predominantly Christian and Druze area of Jaramana, just outside Damascus, killing 11 people, according to state news agency SANA.

The second hit several hours later in the southern Al-Hajar Al-Aswad district, which has seen heavy fighting, causing an unknown number of casualties, state television reported.

The violence came as world powers looked to pick up the pieces of a failed effort for a Muslim holiday ceasefire, with envoy Lakhdar Brahimi in Moscow and due in China on Tuesday as he prepares to present new ideas to the UN Security Council.

"I have said and it bears repeating again and again that the Syrian crisis is very very dangerous, the situation is bad and getting worse," Brahimi said after talks with Russian Foreign Minister Sergei Lavrov.

On Monday, the final day of the four-day Eid al-Adha holiday, the Syrian military launched more than 60 air strikes around the country, said the Syrian Observatory for Human Rights.

"These are the heaviest air strikes since warplanes were first deployed over the summer," the watchdog's director, Rami Abdel Rahman, told AFP.

"The regime is looking to make real gains. There are battles in all of these areas being hit," he said.

Warplanes struck targets around Damascus, the Observatory said, with attacks focused on rebel positions in a northeastern belt where President Bashar al-Assad's regime has been battling to take opposition strongholds.

Dozens of soldiers were wounded and 11 killed in fighting in the area, it said.

The Observatory reported other air raids on villages and towns across the northwestern province of Idlib, where regime forces and rebels have been locked in fierce fighting over the Wadi Deif military base.