A Spanish warship with its guns manned ordered commercial ships to leave British Gibraltar waters on Sunday, the territory's government said.
The warship's crew can be heard in an audio recording of a radio exchange telling vessels anchored at the Rock to "leave Spanish territorial waters".
Royal Navy boats were deployed in response to the incident.
Boats which were ordered to leave remained at the port during the incident, which was branded "foolish" by a spokesman for Her Majesty's Government of Gibraltar.
"There is only nuisance value to these foolish games being played by those who don't accept unimpeachable British sovereignty over the waters around Gibraltar as recognised by the whole world in the United Nations Convention on the Law of the Sea," the spokesman said.
"It seems there are still some in the Spanish navy who think they can flout international law.