BEIRUT (AP) — A strike Thursday by a suspected Iranian-made drone killed a U.S. contractor and wounded six other Americans in northeast Syria, and U.S. forces retaliated with airstrikes on sites in Syria used by groups affiliated with Iran’s Revolutionary Guard, the Pentagon said. Activists said the U.S. bombing killed at least four people.

While it’s not the first time the U.S. and Iran have traded strikes in Syria, the attack and the U.S. response threaten to upend recent efforts to deescalate tensions across the wider Middle East, whose rival powers have made steps toward détente in recent days after years of turmoil.

U.S. Defense Secretary Lloyd Austin said in a statement that the American intelligence community had determined the drone was of Iranian origin, but offered no other immediate evidence to support the claim. The drone hit a coalition base in the northeast Syrian city of Hasaka. The wounded included five American service members and a U.S. contractor.

Austin said the strikes were a response to the drone attack “as well as a series of recent attacks against coalition forces in Syria” by groups affiliated with the Revolutionary Guard.