Since Sept. 11, 2001, Iran has had complex and varied relations with two key players in Afghanistan: the United States and the Taliban. Tehran worked closely with Washington at the 2001 Bonn Conference held after the toppling of Taliban rule. The gathering in Germany was aimed at establishing Afghanistan’s first post-Taliban government, and it succeeded.

But gradually, the US-Iran cooperation turned into confrontation, while the hostility between the Islamic Republic and the Taliban shifted from an initial ‘cold peace’ to greater communication and cooperation. The US withdrawal from Afghanistan this year has reduced the level of Tehran’s sense of insecurity, potentially giving Iran greater freedom of action with regard to the Afghan crisis. Yet this comes as Tehran is now worried about Taliban dominance...