Skirmishes have broken out in Aleppo as rebels pour in to confront regime loyalists in what will be a decisive clash

The pitched battle for Syria's oldest city was edging ever closer to its ancient heart on Saturday, with skirmishes flaring near world-renowned landmarks and once impregnable pillars of state control.

Monuments and security buildings stand cheek-by-jowl in Aleppo, a city of huge importance to the Syrian uprising, where a grand, 1,000-year-old citadel stands not far from a much-feared interrogation dungeon. Yesterday jets were bombing the centre of the city, barely a mile away from the citadel.

Rebel groups claim that, after two weeks of bitter fighting, the city of almost 2.5 million people and linchpin of regime authority is almost within their reach.

However, as rebel reinforcements continued to pour in from elsewhere in the country ahead of an expected push early this week, regime troops were also bolstering defences in areas they continue to hold, primarily in the west and centre of the city.

The rebel force of about 6,000 fighters is being countered by a regime force thought to comprise at least double that number as well as large numbers of the loyalist Shabiha militia, many of whom come from Aleppo and have sworn to defend the city.

Rebel forces have advanced from the north-east and were on Saturday trying to dislodge loyalists who were fighting them on the approaches to the Maysaloon district. Capturing this would open access roads to the city centre, where the fighting flared on Saturday.

It would also, potentially, open a way for rebels, who maintain a foothold in the south-west of the city, to link up with the new arrivals.

Rebel groups say they plan to target the air force intelligence headquarters, among the most feared authorities in Syria's extensive security apparatus. Many of the Aleppo-based rebels claim to have spent time in the building's solitary cells and torture rooms.

"We are saving the tank shells we have for when we get access to the Air Force intelligence headquarters," said Mohammed Karim, from the rebel-held town of Azaz. "We will free the prisoners first, then destroy the building."

Other fighters said getting a foothold in the heart of the city would be difficult. "It could be another three to six months," said Hussein Shmaili, a police captain who defected.

Resting in a house on Aleppo's outer limits, Firas Abu Ayoub said: "The Shabiha are running the checkpoints. They are tough and they are are nasty and they want revenge for Zino Berri."

Berri, allegedly the chief financier and organiser of the Shabiha in Aleppo, was captured with his two sons on Wednesday and savagely gunned down following a brief show trial.

Video footage of the executions taken on mobile phones is being widely shared among rebel groups now advancing on Aleppo. Some rebel commanders are well aware of the damage the executions have done to their cause.

Partly in a bid to rectify the damage, a major from the city of al-Bab, 30km from Aleppo, took the Observer to meet a group of regime prisoners captured in a battle a fortnight ago. All were housed in a classroom on the top floor of a school.

"We were holding them before the Berris were caught," said Major Abu Mohammed al-Asmar. "And they have been treated like kings ever since they got here."

The prisoners, among them three junior Alawite officers and a Shia sergeant, slept on mattresses alongside captured Sunni conscripts. All claimed they would return home if freed.

"I just want a solution," said one of the Alawite officers. "Stability. Who really thinks about sectarianism here? Who doesn't want a state where people's rights are respected?"

None would answer a question about whether the fall of the regime or its continued rule over Syria would make a difference to their lives. And nor would they address a constant refrain among exiled Alawites: that neither rebels nor world leaders could safeguard their futures in the power vacuum that it is likely to follow the end of the regime.

"We don't want guarantees," said a second Alawite officer. "We just need peace."

Later, Major Abu Mohammed said: "We would swap all of these prisoners for just one of our men. The Alawites would return to the army. All of them."

As next week's showdown looms, fighters in the outskirts of Aleppo are continuing to ready for battle. In the early hours of Saturday, 60 members of the al-Bab brigade with bandanas and weapons they had captured from the prisoners now in the schoolhouse left for the frontline.

Aleppo's much-vaunted wealth is on clear display in many well-to-do streets and its commercial districts still appear to be functioning despite the onslaught.

Syrian leader, Bashar al-Assad, said in a statement during the week that the battle for the city would determine the future of Syria.

"That's the first thing he has said that I agree with," Major Abu Mohammed said. "It's also very important for the rest of the Middle East."