Insurgents reached Aleppo, Syria's second city, on Friday, in a swift offensive against Bashar Assad's forces, who are supported by Russian and Iranian allies.

The fighting is some of the deadliest in years, with 255 people, mostly combatants killed, according to the UK-based Syrian Observatory for Human Rights.

It started on Wednesday in areas controlled by the Islamist group Hayat Tahrir al-Sham (HTS). Turkish-backed rebels, calling themselves the Syrian National Army, joined the fighting.

Civilians killed in the fighting

The Syrian military vowed to repel the attack, but even before entering Aleppo, the insurgents wrestled control of more than 50 towns and villages from Assad's forces.

Meanwhile, a military commander of a pro-Syrian militia loyal to the government, Abu Mahmoud Omar, said, "the coming hours will be decisive for the battles after the arrival of large military reinforcements from the Syrian army and allied forces to Aleppo."

The UN said at least 27 civilians were killed in the last three days.

The United Nations Office for the Coordination of Humanitarian Affairs said "more than 14,000 people, nearly half are children, have been displaced" by the violence in the past three days.

"I am alarmed by the deteriorating situation in northwest Syria and the impacts on the lives of civilians," David Carden, deputy regional UN coordinator for humanitarian aid in Syria, said.

"We are getting reports of children with multiple shrapnel wounds from the attacks," he added.

Syrian civil war has never stopped completely

It has been nearly 14 years since the beginning of the Syrian civil war, a conflict that started after a popular revolution was brutally repressed by the Syrian government headed by Assad.

Russia and Iran supported the Syrian government after anti-government protests turned into war.

Turkey has backed opposition groups and established a military presence in northwestern Syria, while the United States has supported Syrian Kurdish forces fighting "Islamic State" (IS) militants in the east.

Since 2020, the conflict has remained largely static, with only low-level clashes between the rebels and Assad's forces.

Turkey and Russia brokered a truce in 2020 with the Syrian government halting a push to retake the rebel-held parts of Idlib.

lo/wd (AFP, AP, dpa, Reuters)