Rebels in Syria have taken control of the “majority” of the country’s second-largest city, Aleppo, according to the British monitoring group Syrian Observatory for Human Rights (SOHR).
Russia launched airstrikes in parts of Aleppo last night for the first time since 2016, the observers added.
SOHR said more than 300 people – including more than 20 civilians – have been killed since the offensive began on Wednesday.
The offensive is the largest against the Syrian government in years and the first time rebels fighting President Bashar al-Assad’s forces have reached Aleppo since they were ousted by the army in 2016.
Aleppo airport and all roads leading to the city have been closed, military sources told Reuters.
The rebels managed to capture the “majority of the city” without encountering significant resistance, the SOHR said early on Saturday.
There was “no fighting” as Syrian regime forces withdrew, a spokesman told the BBC.
“The municipal government, police stations, intelligence agencies – they are empty.
“This has never happened before.”
Earlier on Friday, government forces said they had regained positions in a number of towns in Aleppo and Idlib provinces, following the offensive launched by HTS and allied factions on Wednesday.
Video posted on a channel affiliated with the Islamic militant group Hayat Tahrir al-Sham (HTS) appears to show rebel fighters in vehicles in the city.
BBC Verify geolocated the footage to a western suburb of Aleppo.
More than half a million people have been killed in the civil war that broke out after the government cracked down on pro-democracy protests in 2011.
A range of armed groups opposing the Assad government – including jihadists – took advantage of the unrest to seize parts of the territory.
The Syrian government later regained most of the areas it had lost, with help from Russia and other allies.
Idlib, the last remaining opposition stronghold, is largely controlled by HTS, but Turkish-backed rebel factions and Turkish forces are also based there.
According to SOHR, Syrian and Russian aircraft carried out 23 airstrikes near Idlib on Friday.
The Britain-based monitoring group, which uses a network of sources on the ground in Syria, said four civilians were killed and 19 others injured in the Russian strikes.
The Russian military said it had bombed “extremist forces,” according to Russian news agencies.
Kremlin spokesman Dmitry Peskov expressed support for “the government of Syria to quickly restore order” and said the country’s sovereignty was under attack.
On Friday, a statement on a rebel-affiliated channel said: “Our forces have begun to invade the city of Aleppo.”
Videos verified by the BBC show armed men running through a street about seven kilometers from Aleppo’s medieval citadel in the city center.
Another clip verified by the BBC showed large groups of people walking away with luggage from an area near Aleppo University. That video was recorded three kilometers away from a location where HTS-affiliated media claim rebels entered the city.
Aleppo resident Sarmad told AFP he could “hear the sound of rockets and artillery shelling around the clock.”
“We are afraid that war will break out and we will be driven from our homes again,” the 51-year-old said.
The UN Deputy Regional Humanitarian Coordinator for Syria, David Carden, said he was deeply alarmed by the impact of escalating hostilities on civilians.
“Relentless attacks over the past three days have claimed the lives of at least 27 civilians, including children as young as eight years old,” he said.
Fighting in Idlib had largely subsided since 2020, when Turkey and Russia, Syria’s main ally, brokered a ceasefire to halt a government attempt to retake the province.
But on Wednesday, HTS and its allies said they had launched their offensive to “deter aggression,” accusing the government and allied militias of escalating in the region.
Analysts say one reason they made so much progress is that Syria’s allies, Iran and Hezbollah, have been weakened by Israeli attacks in the region.
Additional reporting by Lina Sinjab in Beirut and Richard Irvine-Brown, Merlyn Thomas and Sofia Ferreira Santos and Paul Brown in London.