A Russian fighter jet flew dangerously close to a manned U.S. surveillance craft in the air over Syria, endangering the lives of all four American crew members, the U.S. military announced Monday.

The Sunday flyby was the latest in a series of incidents in which Russian aircraft harassed American warplanes and drones in the air over Syria. A Russian SU-35v approached a U.S. MC-12 in a manner that could have resulted in a fatal accident, officials said.

Officials did not clarify exactly how close the Russian craft came to the warplane, but there have been myriad examples of similar behavior by Russian forces in recent weeks.

Earlier this month, the U.S. military released footage that showed Russian aircraft flying dangerously close to and deploying flares near several U.S. drones. The videos from consecutive days show Russian SU-35 fighters moving into the flight path of U.S.-operated MQ-9 Reaper drones, forcing them to take evasive maneuvers. It was later revealed that those same drones were used in a strike that killed ISIS leader Usamah al-Muhajir in an airstrike in eastern Syria earlier in the day before facing Russian harassment. The U.S. military has urged Russian forces in Syria to “cease this reckless behavior and adhere to the standards of behavior expected of a professional air force, so we can resume our focus on the enduring defeat of ISIS.”