The UN's Syria peace envoy called Tuesday on the Russian and Turkish presidents to urgently speak to each other to help avert a "bloodbath" in rebel-held Idlib, as a military offensive appears imminent.
Staffan de Mistura appealed to "President Putin and to President Erdogan, ... to make a telephone call," even before they are set to meet with their Iranian counterpart in Tehran on Friday.
"Let's try to avoid that the last probably major battle of the Syrian territorial conflict ... ends in a bloodbath," he told reporters in Geneva, insisting Russia and Turkey held "the key for the soft solution to the Idlib issue".
His comments came with Syrian forces poised to launch an attack on the northwestern province of Idlib, the last major region in Syria still controlled by rebels and jihadists.
After retaking a succession of rebel bastions this year, Damascus has set its sights on Idlib, which is held by a complex array of rebels and jihadists.
The province bordering Turkey is home to nearly three million people, up to half of whom are rebels and civilians transferred en masse after pro-government forces retook formerly rebel-held areas.
A major military operation in Idlib is expected to pose a particular humanitarian nightmare because there is no nearby opposition territory left in Syria to where people could be evacuated.
Turkish and Russian officials have held several rounds of talks hoping to avert an assault, but de Mistura warned Tuesday that the "meetings so far between the Turkish side and the Russian side have not been conclusive".
He stressed the urgency of the situation, pointing to press reports indicating that Syria has set a September 10 deadline for finding a solution before it begins an all-out offensive on the province.
"Time is of the essence," he said.
"That's why our appeal, if I may to president Putin and to President Erdogan to talk and go beyond perhaps technical discussions and (to) find the solution, which can be a soft solution to this crisis."