The UK and Spanish Governments have summoned each other's ambassadors following the entry of Spanish research vessel Ángeles Albariño into the disputed waters off the coast of Gibralter, which both countries claim to be their territory.
According to UK Minister for Europe David Lidington, a Spanish research vessel and a Spanish police ship entered the area without permission.
A Spanish Foreign Ministry spokeswoman said that the Spanish research ship was working alone in Spanish waters, until vessels from the UK Royal Navy and Royal Gibraltar Police showed up to obstruct the ship's work.
"That is when the ship called for help from Spanish police," the spokeswoman said.
The incident is the fourth dispute between the UK and Spain over Gibraltar since 2011.
Europe Minister Gareth Thomas urged the government to carefully consider whether there is a need to station an enhanced Royal Navy presence in Gibraltar's territorial waters.
"Given the continuing disproportionate delays at the Gibraltar-Spain border and the continuing incursions into British Gibraltar territorial waters by Spanish-flagged vessels, I would expect a ministerial level visit from the UK Foreign Office to have already taken place," Thomas said.
Lidington said that, according to the UN convention on the law of the sea, waters around Gibraltar are indisputably British territorial waters under the UK sovereignty, in which only the UK has right to exercise jurisdiction.
"Her Majesty's Government takes a grave view of any attempt by Spain to exert authority or control within British Gibraltar territorial waters and considers such incursions as a violation of our sovereignty. However, the legal fact of the United Kingdom's sovereignty over British Gibraltar territorial waters is not affected by such violations," Lidington added.
Meanwhile, the European Union has urged both countries to work together to solve the border issue.