Iraqi militias who once fought ISIS with U.S. help are now working with Russian and Iranian forces to crush American-backed rebels in the strategic Syrian city of Aleppo, two defense officials have told The Daily Beast.

At least three Shia militias involved in successful battles against ISIS in Iraq—the Badr Brigade, Kata’ib Hezbollah, and the League of the Righteous—have acknowledged taking casualties in fighting in south and southeast Aleppo province. U.S. defense officials confirmed to The Daily Beast that they believe “at least one” unit of the Badr Brigade is fighting in southern Aleppo alongside other Iraqi militia groups. Those groups are backed by Russian airpower and Iranian troops—and all of whom are bolstering President Bashar al Assad’s Syrian Arab Army.

Reports on social media say the Iraqi militias in Syria are armed with U.S. tanks and small arms they procured on the Iraqi side of the border. Those reports could not be independently confirmed.

The presence of militias fighting on behalf of Assad—a dictator that the U.S. has pledged to depose—is yet another reminder of the tangled alliances that the United States must thread as it pursues seemingly contradictory policies in its battles against the self-proclaimed Islamic State. In Iraq, these Shia militias were battling on behalf of the U.S.-backed government. In Syria, they are fighting against an American-supported rebel coalition that includes forces armed by the CIA.

In other words: The forces the U.S. once counted on to take back Iraq’s cities are the same ones the Russians now are counting on to get Aleppo back. And those militias are fighting units of the American-backed Free Syrian Army—including the 16th Division, elements of Jaish al Nasr, and Sultan al Murad—according to Nicholas Heras, a research associate at the Center for a New American Security.

U.S. officials claim not to be alarmed. “On our list of problems, one Badr brigade in Syria is way down there,” one U.S. official explained.

But the role of the Shia militias continues to be controversial. The militias are backed and funded by Iran—Badr, in fact, was created as a branch of the Iranian military. But in Syria, their role is part of the increasingly effective one-two punch of the Russian/Iranian alliance that has given the Syrian government the upper hand in the battle for Aleppo.

U.S. officials agree that without those Iraqi militias, the Syrian Army would be too weak to hold territory on their own.

Read more at The Daily Beast