Fierce fighting was reported in Syria’s two biggest cities – Damascus and Aleppo – as government forces were seeking on Sunday to regain control of rebel-held areas. The army’s elite fourth division, backed by helicopters, has reportedly launched an assault on the capital’s north-eastern suburb of Barzeh, the BBC rep \orts. Troops were also said to have deployed in the western suburb of Mezzeh. Fighting also continued for a third day in Aleppo, where activists said a building had collapsed under tankfire. The violence follows a week in which rebels made major advances, taking control of several parts of Damascus, seizing border crossings and claiming an attack that killed four top security officials, including the defence minister and President Bashar al-Assad’s brother-in-law.Meanwhile, the UK-based Syrian Observatory for Human Rights has reported that at least 19,106 people had been killed since March 2011. They included 13,296 civilians, including those who had taken up arms, as well as 4,861 security personnel and 949 army defectors, it said. The UN said in May that at least 10,000 people had been killed, while in June the Syrian government reported that 6,947 Syrians had died, including at least 3,211 civilians and 2,566 security forces personnel. 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. Activists said residents feared troops were massing for an assault on Salah al-Din, a dense, heavily-populated district with many entrances. There were also reports of violence in the eastern city of Deir al-Zour on Sunday. Witnesses told Reuters that it was being attacked with artillery and rockets from helicopter gunships.President Assad was meanwhile shown on state TV receiving his new armed forces chief-of-staff, Gen Ali Abdullah Ayub, giving him his instructions, and wishing him success in his mission.