(Photo: CGTN)

A UN commission on Wednesday called on rebel groups in Syria's Idlib Province to leave urban areas to protect civilians from any looming assault by government forces. 

The proposal comes after the United Nations' peace envoy for Syria, Staffan de Mistura, last week suggested a deadline be set for fighters in Idlib to pull back from its cities. 

UN agencies and relief organizations 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. 

On Wednesday, the UN Commission of Inquiry on Syria called for jihadists and opposition fighters to leave the most densely populated areas in the region where some three million people live. 

"Most of those terrorist groups and other armed groups, they are in the cities. Perhaps one wonderful scenario is: leave the cities," commission chief Paulo Pinheiro said. 

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 (HTS), 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.

On Wednesday, intermittent artillery fire hit southern districts of Idlib Province and adjacent rebel-held areas of Hama Province, a Britain-based monitor said. But for the second day in a row there were no air raids, after deadly strikes and barrel bombing at the weekend, said the Syrian Observatory for Human Rights. 

On Friday, rebel backer Turkey and government allies Russian and Iran failed to reach an agreement in Tehran to avoid a government assault on Idlib. 

On Tuesday, UN chief Antonio Guterres warned a full-scale battle on Idlib "would unleash a humanitarian nightmare unlike any seen in the blood-soaked Syrian conflict." 

More than 350,000 people have been killed and millions more displaced in Syria's war since it started in 2011.