UNITED NATIONS — 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 stepping down during the transition — a key opposition demand. It only mentions that “the president of Syria 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 communiqué agreed upon by major powers in Geneva calling for the establishment of a transitional governing body for Syria with full executive powers, leading to elections.

Russia’s deputy U.N. ambassador Vladimir Safronkov, who expressed regret that the document had been leaked, told The Associated Press: “It’s our vision — it’s our proposal.”

“And of course we are receptive for proposals from the other side. It’s just Russian contribution, how we launch a political process ... to make parties work together, government and opposition,” he said.