The rebels have pressed a lightning offensive against forces of the Iranian- and Russian-backed Syrian government since Wednesday, the same day a fragile ceasefire took effect in neighbouring Lebanon between Israel and the Iran-backed Hezbollah group, a Damascus ally, after two months of all-out war.

"Hayat Tahrir al-Sham (HTS) and allied factions... took control of most of the city and government centres and prisons", said the Britain-based Syrian Observatory for Human Rights.

HTS, a jihadist alliance led by Al-Qaeda's former Syria branch, controls swathes of the Idlib region, in Syria's northwest, as well as parts of neighbouring Aleppo, Hama and Latakia provinces.

Overnight, Russian "warplanes launched raids on areas of Aleppo city for the first time since 2016", added the Britain-based Observatory, which relies on a network of sources inside Syria.

It raised the death toll in days of clashes to 311 -- 183 from HTS and allied Turkish-backed factions, 100 soldiers and pro-government forces, as well as 28 civilians.

State media reported that four civilians were killed when HTS shelled a student residence in Aleppo, a city of around two million people that was Syria's pre-war manufacturing hub.

Iran-backed militias have a heavy presence in the Aleppo region after providing crucial ground support when the Syrian army -- backed by Russian air power -- recaptured rebel-held areas of the city in 2016.

- Cheering -

An AFP correspondent saw rebels celebrating and cheering inside Aleppo late Friday. Another correspondent saw anti-government fighters in front of the city's landmark citadel.

The Observatory said that "the governor of Aleppo and the police and security branch commanders withdrew from the city centre".

The overnight air strikes coincided with "the arrival of large (rebel) military reinforcements" to the area, the Observatory added, after on Friday reporting the jihadists and their allies had taken more than 50 towns and villages in the north.

Army reinforcements have arrived in Aleppo, a Syrian security official told AFP on Friday, requesting anonymity to discuss sensitive matters, while an army statement said troops had repelled the assault on the city and retaken some positions.

Observatory director Rami Abdel Rahman told AFP early Saturday that rebel fighters swiftly captured swathes of Aleppo without meeting significant resistance, adding "there has been no fighting, not a single shot was fired, as regime forces withdrew."

The jihadists and their allies made other advances in the north, including seizure of the strategically located town of Saraqib, on the road to Aleppo about 40 kilometres (25 miles) southwest, the Observatory had said.

The Russian military said Friday it was bombing "extremist" forces, as Turkey demanded a halt to bombardment on the Idlib region.

Since 2020, the Idlib area has been subject to a Turkey and Russia-brokered truce which had largely been holding despite repeated violations.