PATUXENT RIVER NAVAL AIR STATION, Md.—The U.S. Navy RQ-4A surveillance drone shot down on Thursday was "just days away from retirement," according to several people with knowledge of the matter.

The move comes as tensions between Iran and the United States, which have had strained relations for decades, escalated. Iran reportedly attempted to shoot down another U.S. drone last month, and claimed the surveillance drone shot down this week had entered Iranian airspace. The U.S. insists the drone was in international skies.

Sources close to the Global Hawk drone, who went by the call sign "Black Sparrow," said it was nearing the end of a successful, 20-year Air Force career and hoped to retire to Texas in the coming months.