Syria conflict: Assad troops hit back in Aleppo
Pro-government forces have hit back after rebels seized parts of Syria's economic capital, Aleppo, and tried to move into its historic old city.
Fighter jets and helicopters attacked targets in the east of the city and reports said thousands of troops were being moved to counter the threat.
A general and former aide to President Assad has appeared publicly for the first time since he fled this month.
Brig-Gen Manaf Tlas confirmed he had defected to the Syrian opposition.
In a video statement broadcast on al-Arabiya TV, he appealed to Syrians to "unite to build a free democratic Syria".
At the scene
The military's response marked a sharp escalation in this battle.
Helicopter gunships spun through the skies throughout the day. Sustained artillery and mortar rounds pounded restive neighbourhoods.
But it was what happened late in the afternoon that underlined the grave risk to the government of losing ground in what is Syria's largest city and its economic capital.
First came an unmistakable sound that has so far been absent in this conflict - the roar of fighter jets. What appeared to be Russian-made MiG planes arced through the sky.
We watched as they dropped in, bombing and strafing rebel positions.
Dead and wounded civilians and fighters were taken to hospitals and makeshift clinics as the human cost of this conflict continues to grow.
"Our revolution should be against corruption and oppressors but without destroying the social fabric, for Syria is bigger than individuals," he said, encouraging other Syrian army officers to defect.
Brig-Gen Tlas's decision to abandon Bashar al-Assad had been seen as significant as they were once close friends and he commanded a brigade of the elite Republican Guards.
His whereabouts are still unclear, although he is thought to be in Paris with his family.
Early on Wednesday morning, activists said Syrian forces had fired artillery and rocket barrages on a northern Damascus suburb, forcing hundreds of families to flee the area.
They said that reports suggested that residential blocks of flats had been hit in the attack on al-Tel, Reuters reports.
"Military helicopters are flying now over the town. People were awakened by the sound of explosions and are running away," activist Rafe Alam said.Police siege
Earlier, BBC reporter Ian Pannell described seeing fighter jets attack eastern areas of Aleppo as part of a co-ordinated attack aimed at recapturing districts seized by rebels since the weekend.
It was thought to be the first time that fighter planes had been deployed in such a way during the uprising that began in March 2011.
Civilians as well as rebel fighters were among the dead and wounded, our correspondent said.
Activists said that troops and their tanks were withdrawing from their positions near the Turkish border, at the Jabal al-Zawiya highlands, and were heading towards the city.
At one point, French reporter Florence Aubenas, inside Aleppo, said rebels had surrounded a police headquarters close to the walls of the Old City, which is a world heritage site.Continue reading the main story
In Washington, US Secretary of State Hillary Clinton suggested that territorial gains made by the rebels would eventually result in a "safe haven" that would provide a base for further opposition action.
But reports from opposition activists in the northern province of Idlib, to the west of Aleppo, suggested that Syrian government forces were being moved to reinforce troop numbers in the city.
A rebel source, quoted by Reuters news agency, said thousands of soldiers were leaving the areas of Jebel al-Zawiya and Rami and heading for Syria's most populous city.
Government forces have already regained control of most areas of Damascus that were captured by rebels last week. There were renewed raids in the Tadamon, Qadam and Assali areas of the capital on Tuesday.
According to opposition activists, at least 130 people died in Tuesday's bloodshed across Syria, including 20 people in Aleppo.
In one of the deadliest incidents of the day, opposition activists reported that at least 20 worshippers were killed as they went into a mosque in a village close to the city of Hama.
Troops and militia loyal to President Assad left a roadblock and opened fire on the men who were arriving for evening prayers in Shariaa, one activist told Reuters news agency.
Elsewhere, 10 people were reported killed when a shell hit their car near Hama and a family was said to have died during a bombardment of Deraa in southern Syria.
Foreign journalists work under intense restrictions in Syria so reports by both sides are hard to verify.