An unmanned U.S. military drone was shot down off the coast of Yemen by Houthi militants on Wednesday, according to U.S. officials and the Iran-backed group. It was unclear where exactly the MQ-9 Reaper, a surveillance drone, had been downed. A U.S. defense official told CNN that the Reaper had been over international waters, while a Houthi military spokesperson told the Associated Press that the drone had been in Yemeni airspace. It was also unclear whether the drone was armed. U.S. Central Command is investigating the incident. The episode comes weeks after a U.S. navy warship intercepted four cruise missiles and several drones launched by Houthi rebels, allegedly towards Israel. The Pentagon said Wednesday that there had been at least 41 attacks on U.S. forces in Iraq and Syria by Iran-backed militias, including the Houthis, since Oct. 17, according to The New York Times.