Rebels Seize Control Over Most of Syria’s Largest City in Aleppo

Rebels had seized most of Syria’s largest city, Aleppo, as of Saturday, according to a war monitoring group and to fighters who were combing the streets in search of any remaining pockets of government forces.

The antigovernment rebels said they had faced little resistance on the ground in Aleppo. But Syrian government warplanes responded with airstrikes on the city for the first time since 2016, according to the war monitoring group, the Syrian Observatory for Human Rights.

Aleppo came to a near standstill on Saturday, with many residents staying indoors for fear of what the sudden flip in control might mean, witnesses said. Others did venture out into the streets, welcoming the fighters and hugging them. Some rebels tried to reassure city residents and sent out at least one van to distribute bread.

The rapid advance on Aleppo came just days into a surprise rebel offensive launched on Wednesday against the autocratic regime of President Bashar al-Assad. The developments are both the most serious challenge to Mr. al-Assad’s rule and the most intense escalation in years in a civil war that had been mostly dormant.

The timing of the assault suggested that the rebels could be exploiting weaknesses across an alliance linking Iran to the militant group Hezbollah in Lebanon as well as the Assad regime in Syria and others.

In Aleppo on Saturday, well-armed rebel fighters dressed in camouflage patrolled streets still lined with the ubiquitous posters of Mr. al-Assad. The opposition forces said that although they were in control of nearly the entire city, they had not yet solidified their hold on it.