Damascus: Feared forces headed by President Bashar Al Assad’s brother used helicopter gunships in a new offensive against rebels in Damascus on Sunday, as fighting also raged in Syria’s second city Aleppo.

The Fourth Brigade headed by Maher Al Assad was leading the assault in the Damascus district of Barzeh, triggering a mass exodus of residents from the area, said the Syrian Observatory for Human Rights said.

The Britain-based rights watchdog put the overall death toll from the 16-month uprising in Syria at more than 19,000 — the vast majority of them civilians.

In Damascus, the official news agency Sana said government forces had “cleansed” the Qaboon neighbourhood of “terrorists”, the regime’s term for rebel fighters.

State television ran footage reportedly from Qaboon showing dead bodies as well as weapons, communications equipment and money it said was captured from insurgents.

The Observatory said regime troops had launched an assault on the Barzeh district of Damascus.

“Troops have stormed the northwestern Barzeh district of Damascus with tanks and armed personnel carriers,” the group said, noting snipers had been deployed on rooftops.

“Two helicopters are pounding the Barzeh district, and towers of smoke are rising above the neighbourhood,” the Observatory’s Rami Abdul Rahman told AFP. “The deployment in Barzeh is very heavy.”

“Barzeh is being stormed by the feared Fourth Brigade,” Abdul Rahman added, noting that dozens of residents were fleeing the neighbourhood.

Regime forces also deployed in the outskirts of the Mazzeh district of the capital, he said, adding one person was killed there on Sunday and several were wounded.

Meanwhile, fierce clashes engulfed the districts of Salaheddin and Sakhur in Aleppo, Syria’s commercial hub in the north which has seen heavy fighting since Friday, said Abdul Rahman.

The army’s assault on Salah Al Deen began at dawn, in a bid to reclaim it from rebel hands, an anti-regime activist in the city told AFP.

“Violent clashes have been taking place since the early morning,” the activist said on condition of anonymity.

The fighting came a day after rebel forces battled troops along the borders with Turkey, Iraq and Jordan, seeking to hold or gain control over crossing posts.

Iraqi officials said rebel forces had held onto the Albu Kamal crossing on the Euphrates river after capturing it on Thursday, and fighters had retaken the Rabiyah crossing on the main highway between Aleppo and the Iraqi city of Mosul.

A third crossing between the two countries was still controlled by regime forces.

Rebel forces had taken over the Bab Al Hawa crossing with Turkey on Thursday, but by Saturday evening it was under the control of about 150 foreign fighters who described themselves as Islamists, an AFP photographer reported.

Some of the fighters said they belonged to Al Qaida in the Islamic Maghreb (AQIM), while others claimed allegiance to the “Shura Taliban”.

In Jordan, a security official told AFP that rebel fighters of the Free Syrian Army had tried to overrun the Nassib border crossing, but were repulsed by government troops.

Throughout Saturday, fighting continued across the country, including in the flashpoint central city of Homs, where government forces put down a mutiny at the main prison, leaving two inmates dead, the Observatory said.

In Damascus on Saturday, residents had reported relative calm after days of intense fighting following an attack that killed four senior members of Assad’s regime.

Wednesday’s bombing killed national security chief General Hesham Bekhtyar, Defence Minister General Daoud Rajha, Al Assad’s brother-in-law Assef Shawkat and General Hassan Turkmani, head of the regime’s crisis cell on the uprising.

The regime has responded to the killings with ferocious assaults on rebel strongholds, with the Observatory putting the nationwide death at 302 for Thursday — the highest since uprising broke out in March 2011.

Overall, at least 19,106 people now have been killed since the start of the revolt, according to the watchdog.

That figure includes 13,296 civilians, 4,861 regime troops and 949 defectors, though the Observatory counts civilians who take up arms against the regime in the civilian category.

It is impossible to independently verify death toll accounts from Syria.

Violence in the country has continued as a diplomatic battle over how to respond plays out at the UN, where the Security Council voted Friday to grant a “final” 30-day extension to a troubled observer mission.

UN chief Ban Ki-moon said on Saturday he was “deeply distressed by the rising death toll”, and he warned that the limited extension of the UN mission showed “the onus is above all on the parties, with the Syrian government in the first place, who must stop the killings”.