BEIRUT (AP) – Insurgents breached Syria’s second-largest city Aleppo after blowing up two car bombs on Friday and were clashing with government forces on the city’s western edge, according to a Syria war monitor and fighters. Residents were fleeing neighborhoods on the city’s edge because of missiles and gunfire, according to witnesses in Aleppo.

The insurgents’ advance on Aleppo followed a shock offensive they launched on Wednesday, as thousands of fighters swept through villages and towns in Syria’s northwestern countryside.

The surprise attack added new uncertainty to a region already reeling from the dual wars in Gaza and Lebanon with Israel, and other conflicts including the unresolved Syrian civil war that began in 2011.

It was the first time the city has been attacked by opposition forces since 2016, when they were ousted from Aleppo’s eastern neighborhoods following a grueling military campaign in which Syrian government forces were backed by Russia, Iran and its allied groups.

But this time, there was no sign of a significant pushback from government forces or their allies. Instead, there were reports of government forces melting away in the face of advances, and insurgents have posted messages on social media, calling on troops to surrender. The offensive came as Iran-linked groups, primarily Lebanon’s Hezbollah, who had backed Syrian government forces since 2015, have been preoccupied with their own battle at home.

A ceasefire in Hezbollah’s two-month-long war with Israel came into force Wednesday, the day the Syrian opposition factions announced their offensive. Israel has also escalated its attacks against Hezbollah and Iran-linked targets in Syria during the last 70 days.

The attack on Aleppo came after weeks of simmering low-level violence, including government attacks on opposition-held areas. Turkey, which has backed Syrian opposition groups, failed in its diplomatic efforts to prevent the government attacks, which were seen as a violation of a 2019 agreement sponsored by Russia, Turkey and Iran to freeze the line of the conflict.

Turkish security officials said on Thursday that Syrian opposition groups initially launched a long-planned “limited” offensive toward Aleppo, from where attacks targeting civilians originated. However, the offensive expanded as Syrian government forces began retreating from their positions, the officials said.

The aim of the offensive was to reestablish the boundaries of the de-escalation zone, according to Turkish officials.

The 2016 battle for Aleppo was a turning point in the war between Syrian government forces and rebel fighters since the 2011 protests against Bashar Assad’s rule turned into an all-out war.

Russia and Iran and its allied groups had helped Syrian government forces reclaim control of all of Aleppo that year, after a gruelling military campaign and a siege that lasted for weeks.

As well as backing opposition forces, Turkey has also established a military presence in Syria, sending troops into parts of the northwest. Separately and largely in the east of Syria, the United States has supported Syrian Kurdish forces fighting Islamic State militants.

The Syrian government did not comment on insurgents breaching Aleppo city limits.

But on Friday, the Kremlin said it considers the attack an encroachment on Syria’s sovereignty and supports the quickest possible establishment of constitutional order in the region, Russian presidential spokesperson Dmitry Peskov said at a press briefing.

“Of course, this is a violation of Syria’s sovereignty in this region,” Mr. Peskov said.

He added: “We urge Syria’s authorities to reassert control and restore constitutional order as soon as possible.”

Syria’s Armed Forces said in a statement Friday they have been clashing with insurgents in the countryside around Aleppo and Idlib, destroying drones and heavy weaponry. They vowed to repel the attack and accused the insurgents of spreading false information about their advances.

The Syrian Observatory for Human Rights, a war monitor, said the insurgents detonated two car bombs at the western edge of Aleppo on Friday. The war monitor said the insurgents were also able to seize control of Saraqeb, south of Aleppo, a town strategically located at the intersection of the highways linking Aleppo with Damascus and the coast. Syrian government authorities had diverted traffic from that highway Thursday.

An insurgent commander posted a recorded message on social media calling on Aleppo residents to cooperate with the advancing forces.

Turkey’s state-run Anadolu Agency reported that the opposition insurgents entered Aleppo city center Friday. It said the insurgents “broke through the defense lines of the regime forces along the Hamdaniyya, New Aleppo, and Zahra axis on the outskirts of the city.”

It added the insurgents now control approximately 70 locations in Aleppo and Idlib provinces.

Syria’s state media reported earlier Friday that projectiles from insurgents landed in student accommodation at Aleppo’s university in the city center, killing four people, including two students. Public transportation was also diverted from the main Aleppo-Damascus highway to avoid clashes, the report said.

This week’s advances were among the largest in recent years by opposition factions, led by Hayat Tahrir al-Sham, or HTS, and represent the most intense fighting in northwestern Syria since 2020, when government forces seized areas previously controlled by opposition forces.

Syria’s Armed Forces said the insurgents are violating a 2019 agreement that de-escalated fighting in the area, the last remaining opposition stronghold for years.

The Syrian Observatory said dozens of fighters from both sides were killed in the battles that started Wednesday.

Hezbollah was “the main force” in the government’s control of Aleppo, said Rami Abdurrahman, head of the Observatory.

In a phone call with his Syrian counterpart, Iran’s Foreign Minister Abbas Araghchi described the insurgent attacks in Syria “as a plot orchestrated by the US and the Zionist regime following the regime’s defeat in Lebanon and Palestine.”

Insurgents posted videos online showing they were using drones, a new weapon for them. It was not clear to what extent the drones were used on the battleground.

Turkey’s Anadolu Agency, reporting from Idlib, said insurgents attacked a military airbase southeast of Aleppo city with drones early Friday, destroying a helicopter. It said the opposition groups seized heavy weapons, depots and military vehicles belonging to the government forces during their advance.

Aid groups said the fighting has displaced thousands of families, and forced some services to be suspended. The opposition fighters said their offensive will allow the return of thousands of displaced people who were forced to flee government bombardment in recent weeks.