Syrian insurgents have breached Syria's second-largest city, Aleppo, and are clashing with government forces on the city's western edge, according to a Syrian war monitor as well as fighters themselves.

It is the first time the city has been attacked by opposition forces since 2016, when they were ousted from Aleppo's eastern neighbourhoods by government forces backed by Russia, Iran and its allied groups — a turning point in the country's civil war.

This week, thousands of insurgents have been advancing toward Aleppo in a shock offensive they launched on Wednesday, seizing more than 50 towns and villages along the way, as well as vehicles and heavy weapons from military depots.

The Syrian Observatory for Human Rights, a war monitor, said the insurgents blew up two car bombs at the city's western edge on Friday. Türkiye's state-run Anadolu Agency reported they entered the city centre later that day.

Fighters also advanced on the town of Saraqab, in Syria's north-western Idlib province, a strategic area that would secure supply lines to Aleppo.

One insurgent commander posted a message on social media calling on the city's residents to cooperate with the advancing forces, while other insurgents posted videos showing they were using drones in their advance — a new technology they had not had access to in the earlier stages of their conflict with government forces.

It is not clear to what extent drones are being used on the battleground.

Syrian state media reported earlier that projectiles from insurgents had landed in the student accommodations at Aleppo's university in the city centre, killing four people including two students.

Public transportation to the city had also been diverted from the main highway linking Aleppo to the capital, Damascus, to avoid clashes, the state-controlled media reported.

This week's advances were one of the largest to date made by opposition factions, led by Hayat Tahrir al-Sham (HTS), and came after weeks of low simmering violence.

The fighting is the most intense in north-western Syria since 2020, when government forces seized areas previously controlled by opposition fighters.

The Syrian Observatory for Human Rights said dozens of fighters from both sides have been killed in the battles that started on Wednesday and appear to have caught government forces unprepared, with Iran-linked groups who have backed Syrian government forces since 2015 now preoccupied with their own battle at home.

Hezbollah, the Lebanon-based group that leads Iran's regional alliance, has been locked in a war with Israel for the past year, a war which escalated significantly in September to include an Israeli invasion of Lebanon and an escalation of attacks against Hezbollah and Iran-linked targets in Syria.

A ceasefire was agreed to on Wednesday, but both sides have already accused the other of breaching the agreement.

"Hezbollah was the main force in the government's control of the city [Aleppo]," said Rami Abdulrahman, the head of the Syrian Observatory for Human Rights.

Syria's Armed Forces says the insurgents are violating a 2019 agreement that de-escalated fighting in the area, which has been the last remaining opposition stronghold for years.

Iran's foreign minister called the renewed attacks a "US-Zionist plan", while a Kremlin spokesman said Russia hoped the Syrian government would quickly "restore order" in Aleppo.

Aid groups say the fighting has already displaced thousands of families, and has forced some aid services to be suspended.

The opposition fighters say their offensive will allow the return of thousands of displaced people who were forced to flee government bombardment in recent weeks.

Syria's government, led by Iran-backed dictator Bashar al-Assad, has been battling a range of insurgent groups since 2011, when protests against Mr Assad's rule developed into an all-out civil war.

AP/ABC