An Iranian warplane opened fire on an unarmed U.S. military drone conducting surveillance near Iranian airspace Nov. 1, the Pentagon said Thursday, the first such incident over the Persian Gulf and one that is all but certain to draw attention to Washington’s use of unmanned aircraft, The Washington Post reports.

The MQ-1 Predator drone returned to its base unscathed, even as the Iranian aircraft chased it away from the Islamic Republic’s borders, Pentagon spokesman George Little said Thursday, disclosing details of an incident that the Obama administration chose to keep quiet during the final stretch of the presidential campaign.

The Nov. 1 incident happened at 4:50 a.m. Eastern time, approximately 16 miles from the Iranian coastline, Little said. Under international law, national sovereignty extends for 12 nautical miles.