22 July 2012 Last updated at 03:46 ET
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There have been heavy clashes in several of Syria's main cities
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There has been a third day of fighting in Syria's second city of Aleppo, activists say, the latest focus of the uprising against President Assad.
Thousands of residents are reported to have fled the city, until recently considered a relatively secure government stronghold.
Activists said there had also been clashes in Hama and Deir al-Zour.
In the capital, Damascus, troops recaptured some quarters where rebels had gained a foothold last week.
The rebels also seized border crossings and said they had carried out the bomb attack that killed four top security officials, including the defence minister and Mr Assad's brother-in-law.
ExplosionsAlthough the momentum appeared to be shifting in Damascus, reports from activists in Aleppo said there had been more clashes during the night and early on Sunday between the rebel Free Syrian Army (FSA) and security forces.
They said a building in the Seif al-Dawla district collapsed under tank fire.
Activists said a building in the Seif al-Dawla district collapsed under tank fire
The towns of Atareb, Kafr Karmeen and Abazmo, which lie between Aleppo and the Turkish border to the west, had also been bombarded, they added.
On Saturday, activists said there had been fierce fighting in the Salah al-Din district, and that there had been large explosions and persistent gunfire.
FSA fighters were reported to have stormed all government buildings in the area and raised the rebel Syrian flag above them.
Activists said residents feared troops were massing for an assault on Salah al-Din, a dense, heavily-populated district with many entrances.
The Local Co-ordination Committees, an activist network, said 18 people were killed in Aleppo on Saturday. It put the nationwide death toll at 130, including 34 in Homs province and 28 in Damascus and its suburbs.
'Tactical withdrawal'Meanwhile, state television showed on Sunday pictures of soldiers on the streets of the north-eastern Damascus suburb of Qaboun, after an attack involving heavy artillery, tanks and helicopters.
The streets were largely deserted and strewn with debris and rubble.
State television carried gruesome pictures of many bodies of what it called "terrorists", and showed quantities of arms and ammunition it said were seized, reports the BBC's Jim Muir in Beirut.
"The regime is cutting Qaboun into sectors by deploying tanks on the main roads and crossings to prevent any fighters from moving freely," a rebel fighter told the New York Times.
Government forces have yet to restore their control over the whole city, our correspondent adds.
But activists said the army had distributed leaflets warning people to get out of quarters in the north and south of the capital because of impending bombardments.
At Rukn al-Din, in the north, FSA fighters had carried out a "tactical withdrawal", they added.
There have been heavy clashes in several of Syria's main cities
Continue reading the main story
There has been a third day of fighting in Syria's second city of Aleppo, activists say, the latest focus of the uprising against President Assad.
Thousands of residents are reported to have fled the city, until recently considered a relatively secure government stronghold.
Activists said there had also been clashes in Hama and Deir al-Zour.
In the capital, Damascus, troops recaptured some quarters where rebels had gained a foothold last week.
The rebels also seized border crossings and said they had carried out the bomb attack that killed four top security officials, including the defence minister and Mr Assad's brother-in-law.
ExplosionsAlthough the momentum appeared to be shifting in Damascus, reports from activists in Aleppo said there had been more clashes during the night and early on Sunday between the rebel Free Syrian Army (FSA) and security forces.
They said a building in the Seif al-Dawla district collapsed under tank fire.
The towns of Atareb, Kafr Karmeen and Abazmo, which lie between Aleppo and the Turkish border to the west, had also been bombarded, they added.
On Saturday, activists said there had been fierce fighting in the Salah al-Din district, and that there had been large explosions and persistent gunfire.
FSA fighters were reported to have stormed all government buildings in the area and raised the rebel Syrian flag above them.
Activists said residents feared troops were massing for an assault on Salah al-Din, a dense, heavily-populated district with many entrances.
The Local Co-ordination Committees, an activist network, said 18 people were killed in Aleppo on Saturday. It put the nationwide death toll at 130, including 34 in Homs province and 28 in Damascus and its suburbs.
'Tactical withdrawal'Meanwhile, state television showed on Sunday pictures of soldiers on the streets of the north-eastern Damascus suburb of Qaboun, after an attack involving heavy artillery, tanks and helicopters.
The streets were largely deserted and strewn with debris and rubble.
State television carried gruesome pictures of many bodies of what it called "terrorists", and showed quantities of arms and ammunition it said were seized, reports the BBC's Jim Muir in Beirut.
"The regime is cutting Qaboun into sectors by deploying tanks on the main roads and crossings to prevent any fighters from moving freely," a rebel fighter told the New York Times.
Government forces have yet to restore their control over the whole city, our correspondent adds.
But activists said the army had distributed leaflets warning people to get out of quarters in the north and south of the capital because of impending bombardments.
At Rukn al-Din, in the north, FSA fighters had carried out a "tactical withdrawal", they added.