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 on Tuesday by The Associated Press, makes no mention of Syrian President Bashar al-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 communique 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." The document was reportedly circulated ahead of a second round of talks in Vienna on Saturday among key governments on both sides of the Syrian conflict. De Mistura told reporters after briefing the U.N. Security Council late Tuesday that his message to the 15 members was "one word — momentum." Document's details The Russian document, entitled "Approach To The Settlement of The Syrian Crisis," focuses on both opposition and "terrorist groups," and the need to differentiate between them. It calls for the Security Council to agree to list the Islamic State of Iraq and Syria (ISIS) group as "a terrorist organization," and agreement on an additional list of terrorist groups. When the Syrian government and opposition delegations meet under U.N. auspices, the document says they should agree on a series of steps: Launching a constitutional reform process taking up to 18 months to guarantee "sustainable security and fair balance of interests, rights and obligations of all ethnic and confessional (religious) groups in structures of power and state institutions." Forming a constitutional commission "to embrace the entire spectrum of the Syrian society, including domestic and outside opposition," with the chair agreed by all participants. Submitting the draft constitution to a popular referendum, and "after its approval an early presidential election will be called." Postponing parliamentary elections planned for spring 2016 and scheduling them to be held simultaneously with presidential elections on the basis of the new constitution. Assad was elected to a new seven-year term in 2014 elections that the opposition dismissed as a sham because of the impact of the civil war. Agreeing that the popularly elected president will be commander-in-chief of the armed forces and have "control of special services and foreign policy."