An unlikely fellowship may sprout between the U.S. and Iran as Supreme Leader Ayatollah Ali Khamenei has shown support for U.S. military intervention against ISIS in the Middle-East.

Iran’s foreign ministry official said, according to the BBC, Iran would not co-operate with the U.S. against the Islamic State, but the Ayatollah has authorized his top military commander to work with U.S., Iraqi, and Kurdish military forces to bring a stop to ISIS in the Middle-East.

This comes days after reports saying the Iraqi town of Amerli, which was under ISIS control, was liberated by a coalition of U.S., Iraqi, and Iranian military forces.  The U.S. provided air power, performing airstrikes throughout the town, while Iraqi and Iranian militiamen liberated the town on foot.  Iraqi President Faud Masum confirmed this according to CNN.

As the Economist points out, the militias are not Iranian military forces as we might think of them.  These Iranian militiamen are not directly linked to the Iranian government, but they are either members of the al-Quds, a clandestine arm of Iran’s revolutionary guard, or they are followers of Shia cleric Muqtada al-Sadr who is considered one of the most central religious and political leaders in Iraq.

Al-Sadr is the leader of the Sadrist Movement and had served on many political councils in Iraq.  He had issued a warning to ISIS in June, 2014, saying he and his forces would, “shake the ground under the feet of ignorance and extremism,” according to NBC News.

Shia militias in Iraq are not a new thing as they fought American forces in Iraq when America invaded the country in 2003.  However, now these militiamen seem to be aligning themselves with Western forces in the area to fight the threat of ISIS.

Support from Iran against ISIS should come as no surprise given Iran follows the Shia sect of Islam, while ISIS follows the Sunni sect which views Shia Islam as heretical.