Originally published in the Washington Examiner.

The regime in Iran initially welcomed the triumph of the Taliban over the central government in Kabul, celebrating the humiliation of the U.S., their common foe. While Shiite Iran and the Sunni Taliban hold differing religious ideologies, the two have built strong relations since the Taliban’s initial defeat by U.S. forces in 2001. Anti-Americanism explains this partnership: Both seek to stymie U.S. influence in the Middle East and throughout the Muslim world.

Traditional tensions between the two could, of course, soon reemerge, especially if the Taliban continue to persecute the Persian-speaking Tajiks and the Hazara, the Afghan Shiite minority; interfere with Iran’s access to precious water resources; or allow Afghanistan to become a zone of influence for Pakistan, Turkey, or Qatar, the Islamic Republic’s regional rivals.

Historically, Tehran has had, owing to shifting circumstances, antagonistic and friendly relations with the Taliban. Before the group’s defeat by the U.S. in 2001, the two almost went to war over the Taliban’s killing of Iranian diplomats in 1998 and its brutal treatment of the Hazara.
The Islamic Republic was certainly happy about the Taliban’s fall in 2001, but Tehran’s relationship with the subsequent U.S.-supported Afghan governments was troubled. Kabul’s close cooperation with the West and Tehran’s hostility toward Europe and America meant that Iran and Afghanistan could never develop much trust.

To be sure, Tehran professed friendship but built its own separate network of religious and political influence in Afghanistan, armed and funded Taliban insurgents, and sought to undermine the Afghan government’s control of the Helmand River, which Tehran views as a growing strategic interest given its own severe water shortages. Water shortages have led to widespread protests in Iran and will continue to be a major cause of instability for the clerical regime.

Therefore, securing water from the Helmand River remains a major priority for the Islamic Republic — and Tehran is willing to play hardball to ensure it.

Afghan authorities have accused Iran of bribing Afghan officials to delay the construction of the Helmand River’s Kamal Khan dam, which would impede the flow of water to Iran. A Taliban commander in 2011 claimed that Iran offered him $50,000 to blow up the dam. Many Afghans believe that the Taliban’s repeated attacks on the dam in recent years, resulting in the deaths of security personnel, have been at the order of the regime in Iran.

The Taliban’s renewed persecution of the Tajiks and the Hazara Afghan minority is likely to arouse Tehran’s ire more than anything else, especially if it happens en masse. Last month, Amnesty International reported that the Taliban killed nine ethnic Hazara men in July after it seized control of Afghanistan’s Ghazni province.

Tehran also views Pakistan, Qatar, and Turkey as rivals and will be alarmed by the Taliban’s embrace of them. Pakistan has armed and funded the Taliban and advised it on how it could take power, while Qatar and Turkey have sustained the Taliban’s means of communication with the outside world, including by keeping Kabul’s airport open.

To pressure the Taliban to respect its interests, Tehran may provide funding and arms to the National Resistance Front of Afghanistan, led by Ahmad Massoud, who represents many Tajiks fighting against the Taliban in the Panjshir valley — assuming Massoud can survive long enough to receive Iranian aid. Massoud is the son of the legendary anti-Taliban resistance leader, Ahmad Shah Massoud, who at times received support from the clerical regime.

Tehran can also pressure the Taliban and counter its regional influence through the Fatemiyoun Brigades, a proxy militia consisting of thousands of Afghan Shiite militiamen trained by Iran’s Islamic Revolutionary Guards Corps, who were battle-tested in Syria and Iraq. Iran could try to send them to Afghanistan to fight against the Taliban.

The U.S. defeat in Afghanistan at least for now is a boost for Iran’s theocrats. But the Taliban may prove to be an unstable partner. If the two cannot bury the hatchet, they may discover that two militant Islamic regimes may have sufficient theological, cultural, and geopolitical differences to become ardent foes.

Alireza Nader (@AlirezaNader) is a senior fellow at the Foundation for Defense of Democracies. Navid Mohebbi ( @navidmohebbi) is a policy fellow at the National Union for Democracy in Iran.