Russia has circulated a document on ending the nearly five-year-old Syrian conflict that calls for drafting a new constitution in up to 18 months that would be put to a popular referendum and be followed by an early presidential election.

The document, obtained Tuesday by The Associated Press, makes no mention of Syrian President Bashar Assad's stepping down during the transition — a key opposition demand. It mentions only that the president "will not chair the constitutional commission."

It calls for U.N. special envoy Staffan de Mistura to launch a political process between the Syrian government and "a united delegation of the opposition groups" on the basis of the June 2012 communique agreed on by major powers in Geneva calling for the establishment of a transitional governing body for Syria.