A UN commission on Wednesday called on rebel groups in Syria's Idlib province to leave urban areas to protect civilians from any looming regime assault.
UN agencies and relief organisations have warned repeatedly that any major assault on the province of Idlib, which borders Turkey, could spark one of the worst humanitarian disasters of Syria's seven-year war.
Hany Magally, a fellow panel member, said: "Shouldn't the armed groups move out and spare the civilian population?" Idlib and adjacent areas are largely controlled by Hayat Tahrir al-Sham, an alliance led by Al-Qaeda's former Syrian affiliate, as well as rival rebels. HTS controls the provincial capital Idlib city.
The northwestern region has seen its population almost double with the arrival of Syrians displaced from other parts of the country, many of whom already depend on aid.
"All the other disasters would be minor events compared to what can happen in Idlib," Pinheiro said.
More than 350,000 people have been killed and millions more displaced in Syria's war since it started in 2011.
In the eastern province of Deir Ezzor, US-backed fighters were battling to oust IS from the town of Hajin on the east bank of the Euphrates, the most significant remnant of the jihadists' "caliphate" which once spanned Syria and Iraq.
Despite a number of military campaigns against them, IS fighters are still present in Deir Ezzor, as well as in the vast desert that stretches from Damascus to the Iraqi border.
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