LONDON (Reuters) - Britain accused Spain on Monday of sending a state research vessel on a "serious incursion" into waters around Gibraltar, a British Mediterranean outpost which Madrid wants to reclaim.
A Foreign Office spokesman said the vessel was observed entering British waters on Sunday and illegally conducting sonar surveys.
"The irresponsible actions and dangerous manoeuvring of this vessel were not only unlawful but also presented a significant risk to the safety of Royal Navy personnel at sea," Europe minister David Lidington said in a statement.
No response was immediately available from the Spanish embassy in London.
Gibraltar, ceded to Britain in 1713, has become an increasing source of diplomatic tension since the current Spanish government took office in 2011.
"The waters around Gibraltar are indisputably British," Lidington said. "We will continue to take whatever action we consider necessary to uphold British sovereignty and the interests of Gibraltar, its people, its security and economy."
The Foreign Office, which on Sunday said it was investigating another incident involving a possible incursion by Spanish military jets into British airspace, said Lidington had called Spanish Secretary of State for Foreign Affairs Gonzalo de Benito to express his grave concern.
Reporting by William James; Editing by Michael Holden/Ruth Pitchford