A Spanish Navy patrol ship has made an illegal incursion into UK waters off the coast of Gibraltar.
The naval vessel Infanta Cristina was told to leave the area after being intercepted by the Royal Navy Unit stationed at the British overseas territory.
A spokeswoman for the government of Gibraltar said: "The ship entered British/Gibraltarian territorial waters. It was met by the Gibraltar Squadron and invited to leave."
The incident comes after Spain's Foreign Minister Alfonso Dastis told the UK to calm down after the former Conservative leader Lord Howard suggested Britain could go to war over the Rock.
Tensions are high following draft EU negotiating guidelines circulated by European Council president Donald Tusk, which indicated Madrid would be given a veto over the British overseas territory's participation in a future deal.
While there was no reference to Spain's claim to sovereignty in the EU document, the specific mention of a role for the Madrid government in deciding whether a trade deal would apply to the Rock has caused unease in Westminster.