Iran sees Saudi influence:
http://www.memri.org/report/en/0/0/0/0/0/0/8024.htm
“Regime mouthpieces, both those who support the Rohani government and those who support the Islamic Revolutionary Guards Corps (IRGC) and the ideological camp, accused Saudi Arabia of being behind ISIS activity in Iraq after its defeat in Syria, either on orders from the U.S. and Israel, or independently as a Sunni force combatting Shi’ites.”
Provide the minimum aid to both sides to keep them fighting one another for the next century or until they run out of fighters.