Syrian army shells crashed into southern Damascus yesterday and helicopters fired rockets and machineguns in the heaviest bombardment of the city this month. "The whole of Damascus is shaking with the sound of shelling," said a woman in the Kfar Souseh area.
Troops protected by tanks also swept through the capital on house-to-house raids and executed at least 35 rebel fighters, activists said.
"There are 22 tanks in Kfar Souseh now and behind each one there are at least 30 soldiers. They are raiding houses and executing men," said an opposition activist.
Another activist said the pro-regime shabbiha militia were roaming the streets.
The Syrian Observatory for Human Rights said at least 20 civilians were also killed in Damascus yesterday.
One of the dead was Mohammad Saeed Al Odeh, a journalist at a state-run newspaper who was sympathetic to the revolt. He was said to have been executed by regime forces.
In Aleppo, fighter jets struck the southern district of Sheikh Saeed, the Observatory said, while fighting continued in Deraa in the south.
The violence spilt over into Lebanon on Tuesday, killing seven, and continued yesterday as pro- and anti-Assad gunmen traded fire in Tripoli.
The clashes between Sunnis and Alawites are testing Lebanon's fragile security situation and Najib Mikati, the Lebanese prime minister, urged national unity to insulate the country from "the burning fires all around it".
Mr Mikati expressed concern over "attempts to involve Lebanon more and more" in the conflict in Syria. All parties should consider themselves responsible for the "bloody events in Tripoli" and the "consequences resulting from killing, destruction and bloodshed that will not only impact the city but Lebanon as a whole", he said.
Lebanon's army urged the country's leaders to refrain from "inflaming" the differences among the parties and using the "tense regional situation to settle internal scores". Seven soldiers were injured in yesterday's clashes, it said.
The United Nations said it was concerned about the fallout from the civil war in Syria.
"As the crisis in Syria continues to deteriorate, the situation in Lebanon has become more precarious and the need for continued international support to the government and the Lebanese Armed Forces increasingly important," said the under secretary general Jeffrey Feltman.
Russia accused western powers of "openly instigating" Syrian opposition groups to take up arms. The West "has done nothing" to urge the Syrian opposition to start a dialogue with the government, the foreign ministry said.
* Reuters, Associated Press and Agence France-Presse