Free Syrian Army members, with covered faces and holding weapons, sit by the side of a street in Qaboun district, Damascus
Syrian gunships pounded rebels and troops clashed with insurgents in Aleppo on Friday as world powers voiced fears of an all-out assault and called for "maximum pressure" to prevent a massacre.
Columns of armed forces and armour have poured into Aleppo over the past two days, with troops firing on a string of rebel neighbourhoods in the battle for control of the pivotal northern city, reports AFP.
Amid widespread expectations that an increasingly desperate President Bashar al-Assad will pull out all the stops to secure Aleppo, residents of some areas of the commercial capital fled in fear of a massacre.
The redeployments were "almost complete," a Syrian security official told AFP, while adding that "rebels are stationed in narrow streets, in which fighting will be difficult."
Colonel Abdel Jabbar al-Okaidi of the rebel Free Syrian Army (FSA) told AFP via Skype that "we expect a major offensive at any time."
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."
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 attacked the southwest of the city, in the Salaheddin, Bustan al-Qasr, Sukari, Al-Mashhad and Al-Azamiya neighbourhoods.
In Salaheddin, a rebel told AFP by telephone that residents were fleeing and confirmed helicopters had been firing on the district since daybreak. Troops were on the outskirts of the area and had not yet tried to enter.
Troops also clashed with rebels in the central district of Al-Jamaliya, adjacent to the historic old quarter, as well as in Mahatat Baghdad and in Saadallah al-Jabiri Square.
An AFP journalist said people were starting to go hungry in Aleppo because of a shortage of bread.
He also said the FSA was conserving its ammunition, especially rocket-propelled grenades, in anticipation of the expected tank assault.
The Observatory reported at least four deaths in Aleppo on Friday, among 59 people killed nationwide -- 27 civilians, 17 soldiers and five rebels.
Amid the skirmishes, the rebels captured 150 soldiers and militia members in Aleppo and the northwestern province of Idlib, the Britain-based Observatory said.
On Thursday, pro-government daily Al-Watan said Aleppo would be "the mother of all battles."
"Aleppo will be the last battle waged by the Syrian army to crush the terrorists and, after that, Syria will emerge from the crisis," it said.
A number of powers expressed fears of yet another massacre.
In late May, at least 108 people were killed near the central town of Houla, the United Nations said. On July 12, regime forces killed more than 150 people in the central village of Treimsa, including dozens of rebels, the Observatory said.
White House spokesman Jay Carney rejected on Friday comparisons between Aleppo and Benghazi, the rebel-held Libyan city that was an early focus of the uprising against Moamer Kadhafi.
Kadhafi loyalists launched a major offensive against the Benghazi rebels, and were attacked by an international coalition including the United States enforcing a UN-mandated no-fly zone.
"There were a broader array of issues that allowed for the kind of action that the United States -- you know, the international community, led by the United States, was able to take in Libya," Carney said.
Italy called for "maximum pressure" on Assad to prevent further killings, while UN chief Ban Ki-moon urged his regime to stop its Aleppo offensive.