An Iranian F-4 fighter approached a U.S. Predator MQ-1 unmanned aerial vehicle flying in international airspace over the Persian Gulf earlier recently before turning back following a verbal warning, the Pentagon said.

The F-4 came within about 16 miles of the General Atomics-built MQ-1, which was being escorted by two U.S. military aircraft during the incident, Pentagon spokesman George Little said in a statement.

“All U.S. aircraft remained over international waters at all times,” Little said. “The Iranian aircraft departed after a verbal warning.”

The Predator was unarmed and on a classified surveillance mission, Little said.

In November the Pentagon alleged Iran fired on a Predator operating in international skies. The MQ-1 was not hit, but Iran asserted the drone had violated its airspace.

“Following the incident last November where an Iranian fighter aircraft fired upon an unarmed, unmanned MQ-1, the United States communicated to the Iranians that we will continue to conduct surveillance flights over international waters consistent with long-standing practice and our commitment to the security of the region,” Little said. “We also communicated that we reserve the right to protect our military assets as well as our forces and will continue to do so going forward.”