A former Al Qaeda affiliate took control of the northern Syrian city of Idlib on Sunday, two days after agreeing to end fighting with a rebel group, a monitor said.
"Ahrar Al Sham withdrew from the city of Idlib which is now under the control of Hayat Tahrir Al Sham," said Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights.
"Hundreds of rebels left the city aboard dozens of vehicles heading towards southern Idlib province."
Last week saw fierce clashes between Hayat Tahrir Al Sham and Ahrar Al Sham across much of northwestern Idlib province, including at the key Bab Al Hawa border crossing with Turkey, before a truce was announced late on Friday.
Mr Abdel Rahman said Hayat Tahrir Al Sham had set up checkpoints across Idlib city.
The Observatory also reported two loud explosions in the city, killing one person and wounding 30, but with no further details.
Hayat Tahrir Al Sham and Ahrar Al Shar, which is supported by Turkey and some Gulf countries, were once allies and fought alongside each other to capture most of Idlib province from the Syrian government in 2015.
But analysts say growing tensions over the past two months have been exacerbated by Hayat Tahrir Al Sham's fears of a plan to expel the internationally designated "terror" group from the province.
Idlib is one of the last Syrian provinces still beyond regime control.
The fall of Idlib city, the provincial capital, to the extremists is symbolic and comes after the Observatory said they captured "more than 31 towns and villages" across the province over the past two days.
The bloodless takeover of the towns and villages came after Friday's truce announcement.
Hayat Tahrir Al Sham is dominated by the Jabhat Fatah Al Sham faction, which was previously known as Jabhat Al Nusra before renouncing its ties to Al Qaeda.
The fighting that erupted on Tuesday last week killed around 100 people including 15 civilians, the Observatory had said on Friday.