BEIRUT – Insurgents entered Syria’s second-largest city, Aleppo, after detonating two car bombs on Friday and clashed with government troops on the city’s western edge, according to a Syria war monitor and fighters.

According to witnesses in Aleppo, residents fled neighborhoods on the outskirts of the city because of rocket fire and gunfire.

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

The surprise attack created new uncertainty in a region already reeling from the twin 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 was attacked by opposition forces since they were toppled in 2016 after a grueling military campaign in which Syrian government troops were backed by Russia, Iran and their allied groups.

This time there was no sign of significant resistance from government forces or their allies. Instead, there were reports of government troops melting away in the face of progress. Insurgents have posted messages on social media calling on troops to surrender. The offensive came as Iran-linked groups, most notably Lebanon’s Hezbollah, which had supported Syrian government forces since 2015, were preoccupied with their own fighting at home.

A ceasefire in Hezbollah’s war with Israel came into effect on Wednesday, the day Syrian opposition factions announced their offensive. Israel has also stepped up its attacks against Hezbollah and Iran-linked targets in Syria over the past 70 days.

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

Turkish security officials said on Thursday that Syrian opposition groups had initially launched a long-planned “limited” offensive against Aleppo, from where attacks on civilians took place. But the offensive expanded as Syrian government forces began withdrawing from their positions, the officials said.

According to Turkish officials, the aim of the offensive was to restore the boundaries of the de-escalation zone.

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

Russia, Iran and their allied groups helped Syrian government forces regain control of all of Aleppo this year after a grueling military operation and a weeks-long siege.

In addition to supporting opposition forces, Turkey has established a military presence in Syria and deployed troops to parts of the northwest. Separately, and largely in eastern Syria, the United States has supported Syrian Kurdish forces fighting Islamic State militants.

The Syrian government did not comment on the insurgents who broke through the city limits of Aleppo.

But on Friday the Kremlin said it viewed the attack as an encroachment on Syria’s sovereignty and supported the establishment of a constitutional order in the region as quickly as possible, Russian presidential spokesman Dmitry Peskov told a news conference.

He added: “We urge the Syrian authorities to restore control and restore constitutional order as soon as possible.”

Syrian forces said in a statement on Friday that they had clashed with insurgents in the countryside around Aleppo and Idlib, destroying drones and heavy weapons. 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 on Friday on the western edge of Aleppo. The war monitor said the insurgents had also managed to take control of Saraqeb south of Aleppo, a city strategically located at the crossroads of highways linking Aleppo to Damascus and the coast. Syrian government authorities diverted traffic from this highway on Thursday.

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

Turkey’s state-run Anadolu Agency reported that insurgents “have broken through the defense lines of regime forces along the Hamdaniyya, New Aleppo and Zahra axes on the outskirts of the city.” It added that the insurgents currently control about 70 locations in Aleppo and Idlib provinces.

Syrian state media reported on Friday that insurgent projectiles struck student accommodation at Aleppo University in the city center, killing four people, including two students. In addition, public transport was rerouted from the main Aleppo-Damascus highway to avoid collisions, the report said.

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

Syrian forces said the insurgents were violating a 2019 agreement that deescalated fighting in the region, the last remaining opposition stronghold in years.

The Syrian Observatory said dozens of fighters from both sides were killed in the fighting that began on Wednesday. Hezbollah is “the main force” in the government’s control of Aleppo, said Rami Abdurrahman, head of the Observatory.

Insurgents posted videos online showing them using drones, a new weapon for them. The Turkish Anadolu Agency reported from Idlib that insurgents attacked a military airfield southeast of the city of Aleppo with drones early on Friday, destroying a helicopter. It said the opposition groups seized heavy weapons, depots and military vehicles from government troops as they advanced.

Aid groups said the fighting had displaced thousands of families and forced the suspension of some services. The opposition fighters said their offensive would allow the return of thousands of displaced people who were forced to flee government bombings in recent weeks.

Deeb writes for the Associated Press. AP writers Suzan Fraser in Ankara, Turkey and Albert Aji in Damascus, Syria contributed to this report.