Syria rebels and regime troops mass in Aleppo for the battle that could decide the war

Thousands of civilians flee as Assad steps up air strikes in bid to destroy opposition foothold

Syria's most populous city was braced for an all-out battle last night as regime tanks and columns of soldiers began to mass on its outskirts and rebel forces poured in.

Thousands of army soldiers were said to be moving towards Aleppo last night after being pulled from positions in the surrounding countryside.

Syria's commercial capital holds huge strategic value for the Free Syrian Army (FSA), which has said it hopes to make it "their Benghazi" – a reference to the Libyan city from which the rebels who ousted Muammar Gaddafi launched their offensive.

After nearly a week of clashes, the opposition yesterday claimed to be in control of several neighbourhoods, including Kalasseh, Al Shaar and Salaheddine, but it said helicopter gunships and jet planes were strafing rebel positions, sending tens of thousands of residents fleeing.

Once a bastion of support for President Bashar al-Assad, and run by merchant elites who have benefited handsomely from his rule, his regime appeared determined not to let the city fall into rebel hands. If it were to fall, Aleppo would give the FSA a firm foothold in the north, a geographical base which analysts say could tip the fight in their favour.

"There are 80 tanks on their way and more than 2,000 men," said Mohammed Saeed, a local activist. "The people are very worried, there is panic and most of the people in neighbourhoods with fighting have left their houses."

Claiming that as many as 5,000 rebel fighters are already in Aleppo, activists and FSA sources said many more were on their way from surrounding areas already under rebel control.

The police station in Kalasseh was burnt down while another in Al Shaar was taken over by rebel forces, activists said, posting a video on the internet which showed at least a dozen men kneeling with their hands bound outside the building. The activists said that warplanes – which they claimed were either Russian-made MiG 27s or MiG 23s – flew over the city three times, attacking rebel targets, while helicopter gunships were a more frequent presence.

Air raids by fighter jets were reported for the first time on Tuesday, but the regime appeared to have widened its use of the tactic yesterday, with ITN reporting their use in the Damascus suburb of Douma.

Though the Syrian regime is largely back in control of the capital it has continued its campaign to purge rebel neighbourhoods.

In some extremely graphic footage purported to be from the district of Al Qabon, bodies were filmed being pulled out of a building and heaped on to the street. One male victim had had his fingers cut off. The man filming the scene counted five bodies before entering the house, panning across blood pooled in the corridor before running out retching. Returning he filmed two dead men sprawled on the floor. In another building he found four bodies, one mutilated.

Bloodshed was reported up and down the country, with fierce fighting further south in the rebel stronghold of Homs, where activists said T-72 tanks were pounding the city.

There were further diplomatic defections with the charge d'affaires in Cyprus and her husband, the ambassador to the United Arab Emirates, denouncing the regime.

President Assad appears to be unleashing all his firepower to bring the country under control. Russia yesterday joined Western nations in condemning Syria's recent threat to use chemical weapons against foreign forces. The deputy Foreign Minister Mikhail Bogdanov made clear Russia's position on "the inadmissibility of any threats of the use of chemical weapons" during a meeting with Syria's ambassador to Moscow.