The UN mediator in the Syrian conflict, Staffan de Mistura, says he believes there is a fresh opportunity to resolve the country’s crisis.
He said truce measures could succeed because of the common threat from IS militants, as well as a growing weariness with conflict.
The UN has called for “freeze zones” to halt fighting and improve aid, the BBC reported.
More than 200,000 people have died in Syria’s conflict, now in its fourth year.
Rebel groups such as IS and the al-Qaeda-aligned Nusra Front have been fighting among themselves, as well as against forces loyal to President Bashar al-Assad.
The conflict broadened this year with a US-led coalition launching air strikes in Syria, mainly targeting IS fighters.
In an interview with the BBC, Lyse Doucet in the war-torn Syrian city of Homs, de Mistura said the rise of IS was “a new factor which can turn into the possibility of looking at this conflict in a different way”.
He said rival sides that viewed IS and the Nusra Front as a common enemy were beginning to question if the conflict was “giving an opportunity to someone else to take advantage of it”.
Moreover, he said, there was a growing realization that attempts to win the conflict by force were not working.
The UN plans call on all sides to freeze - or de-escalate - the violence through local truces to allow for the movement of humanitarian aid.
“Saying having a peace plan would be ambitious and delusionary,” de Mistura told the BBC. “But I do have an action plan, and the action plan starts from the ground - stop the fighting, reduce the violence.”
Earlier, President Assad said his government was considering the UN truce plan for Aleppo, which is split into rebel and government-controlled areas.
De Mistura discussed the plans with Assad during talks in the Syrian capital, Damascus, during the envoy’s second visit to the country since his appointment in July.
Local ceasefires or “incremental freeze zones” have had some effect in other areas of Syria and de Mistura earlier indicated Aleppo would be a good candidate.
The state news agency Sana quoted Assad’s office as saying that the president “considered the de Mistura initiative worth studying and trying to work on in order to attain its aims to return security to the city of Aleppo”.
Aleppo has been racked by fighting since July 2012.
Previous UN envoys have failed to negotiate a full ceasefire between the government and militant groups
