Britain has protested in the "strongest terms" after an "illegal incursion" by a Spanish Guardia Civil vessel into British territorial waters around Gibraltar.
Europe Minister David Lidington said in a statement that a Guardia Civil officer on board the vessel fired a weapon during the incident on Sunday.
Lidington said he had sought assurance from his Spanish counterpart that action would be taken to ensure there was no repeat of the incident.
"I spoke today with Spanish minister for the European Union, Inigo Mendez de Vigo, in order to protest in the strongest terms following an incident on June 23 in British Gibraltar Territorial Waters (BGTW). During an illegal incursion by a Guardia Civil vessel, a Guardia Civil officer fired a weapon," he said.
"I made clear that the discharge of a weapon in or near Gibraltar is completely unacceptable. I urged Senor Mendez de Vigo to investigate urgently and to take action to ensure that this will not happen again."
Lidington said he also instructed the British charge d'affaires in Madrid to protest in person to the Spanish Ministry of Foreign Affairs and to demand a full explanation.
The incident is understood to have involved a chase by the Guardia Civil vessel which pursed a Gibraltarian jet ski into British Gibraltar territorial waters.
Onlookers were said to have seen large rubber or plastic baton rounds being fired from the Guardia Civil and splashing into the water.
The incident took place off a popular beach and it is understood that the Royal Gibraltar Police took statements from a number of witnesses, including the individual on the jet ski.
A video posted on the local Gibraltar website Vox appears to show the incident.Suggest a correction