Rebel forces in Syria have taken control of the "majority" of the country's second-largest city, Aleppo, according to the UK-based monitoring group Syrian Observatory for Human Rights (SOHR).

Russia launched air raids in parts of Aleppo overnight into Saturday 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 started on Wednesday.

The offensive is the largest against the Syrian government in years and the first time rebels fighting the forces of President Bashar al-Assad have reached Aleppo since being forced out by the army in 2016.

Syria's military confirmed on Saturday that rebels had entered "large parts" of the city and dozens of soldiers had been killed or injured in the fighting.

In a statement, it said troops had been withdrawn from Aleppo temporarily "to prepare a counteroffensive".

Aleppo's airport and all roads leading into the city have been closed, military sources told Reuters news agency.

The rebels were able to capture the "majority of the city" without meeting significant resistance, the SOHR said early on Saturday.

There was "no fighting" as Syrian regime forces withdrew, a spokesperson told the BBC.

"The city council, police stations, intelligence offices - 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 Islamist militant group Hayat Tahrir al-Sham (HTS) appears to show rebel fighters in vehicles inside the city.

BBC Verify has geolocated the footage to a western suburb of Aleppo.

AFP said one of its reporters had seen "anti-government fighters" in front of the city's landmark citadel on Friday.

More than half a million people have been killed in the civil war that erupted after the government cracked down on pro-democracy protests in 2011.

An array of armed groups opposed to the Assad government - including jihadists - took advantage of the turmoil to seize swathes of territory.

The Syrian government - with help from Russia and other allies - later retook most the areas it had lost.

Idlib, the last remaining opposition stronghold, is mostly controlled by HTS, but Turkish-backed rebel factions and Turkish forces are also based there.

Syrian and Russian planes carried out 23 air strikes near Idlib on Friday, according to SOHR.

The UK-based monitoring group, which uses a network of sources on the ground in Syria, said four civilians were killed and 19 others were injured in the Russian strikes.

Russia's military said it had bombed "extremist forces", according to Russian news agencies.

Kremlin spokesman Dmitry Peskov expressed his support for "the government of Syria to quickly restore order" and said the country's sovereignty was under attack.

(Source:BBC)