A senior U.S. official told Reuters that the U.S has launched an airstrike on pro-Assad forces in Syria.

Pro-Syrian regime forces were reportedly in a “de-confliction zone,” a prohibited¬†action. U.S. forces in the ground then called in airstrikes after they refused to leave the area.

But Pentagon officials say the policy toward Syria has not changed.

The strikes took place near the town of At Tanf, on the border with Iraq, Reuters reports.

The Russians and the Iranians back the dictator Assad while the U.S. backs the rebels fighting against Assad’s forces.

As Reuters explained: “A Western intelligence official, speaking on condition of anonymity, said the strike sent a strong message to Iranian-backed militias that have been spearheading the advance that they would not be allowed to reach the Iraq border from Syria.”