UN Syria envoy Staffan de Mistura has been invited to peace talks convened by Russia, Turkey and Iran in the Kazakh capital Astana next week, his spokeswoman Yara Sharif said on Thursday.
A UN statement said de Mistura himself would lead the UN team in Astana because of the complexity and importance of the issues likely to be raised.
The Astana talks, which will start on January 23, are being organised by Iran, Russia and Turkey with Syrian rebel leaders and Bashar al-Assad representatives expected to meet face to face.
De Mistura has said he hopes Astana will support the next round of UN-led talks he plans in Geneva from February 8.
UN Senior Adviser on Syria Jan Egeland said Russia, Turkey and Iran had taken on an immense responsibility as guarantors of a process that aimed to enable a new beginning for the civilian population.
Egeland said the upcoming peace talks were also a chance to save the people of Idlib, a rebel-held town which received 36,000 people evacuated from eastern Aleppo, from another "big storm."
"Idlib would be the symbol of a place that can be saved if this becomes the year of diplomacy, 2017, after six years of failed diplomacy," he said.
Intense fighting in Deir Ezzor
The fighting was still "tremendous" in many places, including the Wadi Barada valley near Damascus, and around the desert town of Deir Ezzor, where about 93,000 civilians have been cut off since Sunday after Daesh captured the drop zone for humanitarian supplies.
The town has food for a few weeks, and the hospital treating wounded came under fire and had to be moved, Egeland said.
The four besieged towns of Madaya, Zabadani, Foua and Kefraya were now a "disaster" and people were now dying routinely because of the lack of medical attention, he said.
He also complained the bureaucratic "quagmire," which includes coming to agreements with different actors and getting permits, prevents the effective implementation of humanitarian assistance programmes.
Egeland and the UN's World Food Programme (WFP) also said food supplies in the desert town of Deir Ezzor, besieged by Daesh since 2015, could run out in a few weeks.
WFP had to suspend humanitarian air drops in Deir Ezzor on Sunday because of heavy fighting after a fierce assault by Daesh.
The 93,000 people living under siege in Deir Ezzor "really do not have any lifeline other than relief by air", Egeland said.
TRT World's Shamim Chowdhury has more details from Gaziantep.