U.S. military officials say an Iranian drone harassed and nearly collided with a Navy attack jet Tuesday as it prepared to land on an aircraft carrier in the Persian Gulf.

The two aircraft — an Iranian QOM-1 and a U.S. F/A-18E Super Hornet — came within 100 feet of one another as the Super Hornet circled above the USS Nimitz, officials said, noting the pilot was forced to make a sudden maneuver to avoid crashing into the drone.

Tuesday’s incident, which occurred in international airspace, U.S. officials said, marks the latest in a series of threatening encounters between the two militaries.

In a statement, U.S. Central Command declared the incident “unsafe and unprofessional,” calling it a breach of international maritime customs and laws. It’s the Navy’s 13th such run-in with Iranian military forces this year, officials said.

It’s unclear whether the drone was armed or whether Iranian military officials communicated with the Americans, who say they made repeated radio calls warning the drone’s operator to keep away.

In recent months, U.S. jets operating in Syria have shot down armed Iranian drones that moved too close to American ground troops. And there have been numerous close calls involving U.S. and Iranian vessels at sea.

This latest encounter comes two weeks after the crew on a Navy patrol boat fired warning shots at an Iranian military ship that had come within 150 yards of the Americans as they conducted training in the Persian Gulf.

Last year, the Pentagon documented 35 hostile interactions with Iranian forces, up from 23 in 2015.