The US Navy on Tuesday claimed Iran’s Islamic Revolutionary Guard Corps seized and later let go of an American sea drone in the Arabian Gulf.
Commander Timothy Hawkins, spokesman for the Navy's Mideast-based 5th Fleet, said an IRGC ship on Monday temporarily took control of the Saildrone Explorer.
Mr Hawkins said the vessel was towing the drone as a US Navy ship and helicopter approached.
A statement from Gen Michael 'Erik' Kurilla, of the US Central Command, said "this incident once again demonstrates Iran's continued destabilising, illegal and unprofessional activity in the Middle East".
He also commended naval forces on the USS Thunderbolt for their quick response, involving calling a helicopter to the scene of the incident.
Mr Hawkins told the Associated Press that the Navy had called repeatedly to the Iranians, who ultimately let the drone go.
A US Navy statement said the incident took place over the course of four hours and the sea drone, which it admitted belonged to the US government, did not host classified information or technology.
Iran did not immediately acknowledge the incident, which came amid heightened tension between Washington and Tehran, with the nuclear deal with world powers seemingly in disarray after a series of failed talks.