The UN envoy for Syria has hosted key diplomats from Iran, Russia and Turkey to discuss work towards rewriting the country’s constitution, amid concerns about a military offensive on rebel-held Idlib province.

The talks led by Staffan de Mistura ended with little comment to reporters at the UN offices in Geneva, and offered a sideshow to concerns about a looming battle for the northern province — the last remaining rebel stronghold in Syria after seven years of war which is home to three million civilians.

Mr de Mistura’s spokesman, Michael Contet, said any debriefing by the envoy about the meeting will be “reserved” for comments he plans to make to the UN Security Council next Tuesday.

A Syrian government air strike in Hobeit village, near Idlib
A Syrian government air strike in Hobeit village, near Idlib (Syrian Civil Defence White Helmets/AP)

On Monday, the head of the UN humanitarian agency, Mark Lowcock, warned that Idlib could see “the worst humanitarian catastrophe, with the biggest loss of life of the 21st century”.

Iran and Russia have backed a military campaign on Idlib involving Syrian President Bashar Assad’s forces, despite Turkey’s pleas for a ceasefire.

Hossein Jaberi Ansari
Hossein Jaberi Ansari (Salvatore Di Nolfi/Keystone/AP)

Before Tuesday’s meeting, Hossein Jaberi Ansari, a special envoy for Iran’s foreign minister, said a “good result” could emerge. Asked whether Iran shared concerns about a possible humanitarian catastrophe in Idlib, he replied: “We are worried too. We are trying to avoid this.”

Russian President Vladimir Putin’s special envoy for Syria, Alexander Lavrentiev, declined to answer a question on his way into the talks about whether Russia would stop its air strikes.

Russia’s special envoy on Syria Alexander Lavrentiev
Russia’s special envoy on Syria Alexander Lavrentiev (Salvatore Di Nolfi/Keystone/AP)

Mr de Mistura met members of the three delegations informally on Monday.

The talks are set to focus on creating a constitutional committee under Syria’s Russian and Iranian-backed government.

Russia, Turkey and Iran have been working together as “guarantors” for a series of talks around ending Syria’s war. Turkey has taken in 3.5 million refugees from its neighbour.

On Monday, air strikes on Idlib and Hama provinces forced some people to flee their homes, according to the Britain-based Syrian Observatory for Human Rights.

On Tuesday, a monitoring group said 21 pro-government gunmen had been killed in clashes with the Islamic State group in southern Syria.

The Syrian Observatory for Human Rights said the fighters died in clashes with the militants on Monday night in the Safaa region in the Syrian desert.

Government forces backed by local and regional militias have been battling the militants for weeks in the countryside north of Sweida since the militants ambushed the city and its surrounds in July.

The militants are holding 30 civilians captive since kidnapping them in the assault. They are believed to be holding them in the Safaa area.