US sees Assad staying in power until at least March 2017: Report

"Asad relinquishes presidency; inner circle departs," the US timeline said, according to the AP, using the American government’s spelling for the Syrian leader.

Based on a UN-endorsed plan laid out at an international conference in Vienna in November, political transition in Syria would include presidential and parliamentary elections next August, the report said. 

Syria's new political process is slated to start next month. In its first step, the government and opposition will begin peace talks in Geneva on 25 January, a date set by Staffan de Mistura, the UN's special envoy for Syria. 

During the transition period, the country will be run by a transitional governing body that would be formed after a security committee is created in April. It would consist of Assad representatives and opposition members, the document said.

In May, the Syrian parliament would be disbanded, according to the timeline.

"The [UN] Security Council would recognise the new transitional authority and lay out the transition's next steps," said AP.

"These include major political reforms, the nomination of an interim legislature and an international donors' conference to fund Syria's transition and reconstruction."

Between May and November of this year, the sides will draft a new constitution. Syrians would then vote on the document in a popular referendum next January, according to the timeline. Two months later, Assad is expected to step down. 

Syria's new government would assume full powers from the transitional body after parliamentary and presidential elections in August.

But it is unclear how Syria's opposition will react to the report, with many key rebel factions insisting on Assad stepping down. In December, during a meeting in Riyadh, many key rebel groups agreed that they would talk to the Syrian government, but not to Assad or his top aides. 

"The aim of the political settlement is to create a state based on the principle of citizenship without Bashar al-Assad or figures of his regime having a place in it or any future political arrangements," the group of rebel factions said in a statement issued at the time. 

The Syria conflict, which will enter its sixth year in early 2016, has left more than 250,000 people dead and turned the country into the world's largest source of refugees and displaced persons, according to the UN. 

Nearly 8 million Syrians are internally displaced and more than 4 million have fled to nearby countries since the conflict started.