Syrian anti-regime groups led by the Hayat Tahrir al-Sham (HTS) breached Aleppo and began entering the city amid clashes with Damascus' forces, sources said Friday.

The armed groups have been approaching Aleppo, Syria’s second-largest and retained by Bashar Assad’s regime, for days and have seized several towns and villages along the way.

The Syrian Observatory for Human Rights, a war monitor, said the groups blew up two car bombs at the city's western edge on Friday.

A HTS commander issued a recorded message posted on social media calling on the city's residents to cooperate with the advancing forces.

Fighters also advanced on the town of Saraqab, in northwestern Idlib province, a strategic area that would secure supply lines to Aleppo.

This week's advances were one of the largest by anti-regime factions led by the HTS and came after weeks of simmering violence.

It is the most intense fighting in northwestern Syria since 2020 when regime forces seized areas previously controlled by opposition fighters. It is also the largest offensive by anti-regime fighters in the city since they were ousted from its eastern area in 2016.

The war monitor Syrian Observatory for Human Rights said dozens of fighters from both sides have been killed in the battles that started Wednesday. The armed groups have seized control of more than 50 villages in their advance, which seems to have caught the regime forces unprepared.

The agency also reported that the fighters attacked a military air base southeast of Aleppo city with drones early Friday, destroying a helicopter.

The 2016 battle for Aleppo was a turning point in the war between Syrian regime forces and anti-regime fighters since the 2011 protests against 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 grueling military campaign and a siege that lasted for weeks.

Türkiye has been a main backer of an array of opposition forces, excluding the HTS, and its troops have established a military presence in parts of northwestern Syria.