Syrian gunships pounded rebel positions in Aleppo yesterday and troops clashed with insurgents as government forces readied an all-out assault billed as the “mother of all battles”.

Amid widespread expectations that an increasingly desperate President Bashar al-Assad will pull out all the stops to secure Syria’s commercial capital, residents of some districts fled in fear of a massacre.

Ground troops, artillery and armour have been massing since Thursday on the outskirts of Syria’s second city, and a security source said that by yesterday deployments were “almost complete”.

“Rebels are stationed in narrow streets, in which fighting will be difficult,” a security source said.

Syrian Observatory for Human Rights director Rami Abdel Rahman said: “The question is, to what extent will regime troops resort to excessive use of force, because if this is the case, there will be hundreds of deaths.”

Global powers have also expressed fears of a potential slaughter” in Aleppo and called for maximum pressure to prevent it.

Aleppo has been the scene of fierce fighting since rebels launched a major offensive on July 20 from rear bases across the nearby border with Turkey.

The Observatory said helicopter gunships were attacking positions in the southwest of the city, in the Salaheddin, Bustan al-Qasr, Sukari, Al-Mashhad and Al-Azamiya neighbourhoods. It reported four deaths in Aleppo yesterday morning, among at least 29 killed nationwide.

In Salaheddin, a rebel told AFP by telephone that residents were fleeing and confirmed that helicopter gunships had been firing on the area since 6 a.m.

He said troops were on the outskirts of the neighbourhood but had not yet tried to enter.

“We expect a major offensive at any time,” Colonel Abdel Jabbar al-Okaidi, a spokesman for the rebel Free Syrian Army (FSA), told AFP via Skype.

Amid the skirmishes, the rebels said they had captured 100 soldiers and militia members in Aleppo, purportedly showing them in a video filmed by a man describing himself as a member of the FSA.

French Foreign Ministry spokesman Bernard Valero told AFP that “with the build-up of heavy weapons around Aleppo, Assad is preparing to carry out a fresh slaughter of his own people”.

Noting the massing of forces, US State Department spokesman Victoria Nuland said “this is the concern that we will see a massacre in Aleppo, and that’s what the regime appears to be lining up for.

“Our hearts are with the people of Aleppo. And again, this is another desperate attempt by a regime that is going down to try to maintain control, and we are greatly concerned about what they are capable of in Aleppo.”

In Geneva, UN human rights chief Navi Pillay spoke of atrocities in the regime’s ongoing battle to cleanse Damascus of rebel elements and said Aleppo was also at risk.

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