WASHINGTON - The Obama administration's best-case scenario for political transition in Syria does not foresee Bashar Assad stepping down as the country's leader before March 2017, outlasting Barack Obama's presidency by at least two months, according to a document obtained by The Associated Press.

An internal timeline prepared for U.S. officials dealing with the Syria crisis sets an unspecified date in March 2017 for Assad to "relinquish" his position as president and for his "inner circle" to depart. That would be more than five years after Obama first called for Assad to leave.

The timeline is based on a broad U.N.-endorsed plan that was initially laid out at an international conference in Vienna in November. Syria, according to that strategy, would hold elections for a new president and parliament in August 2017 — some 19 months from now. In the interim, Syria would be run by a transitional governing body.

Countless hurdles lie ahead for this latest blueprint for ending five years of conflict that has killed more than a quarter-million people, created the worst refugee crisis in Europe since World War II and allowed the Islamic State group to carve out a would-be caliphate across parts of Iraq and Syria.

Not the least of those hurdles is the growing rift between Sunni-led Saudi Arabia and Shiite-ruled Iran, which back opposite sides in the Syria conflict and had to be lobbied heavily to agree to meet in Vienna to craft a way forward for the war-torn country. Saudi Arabia executed a prominent Shiite cleric and then severed diplomatic relations with Iran this week after its embassy in Tehran was stormed by a mob protesting the death.(AP)