Britain has summoned Madrid's envoy to London over an alleged incursion of a Spanish vessel in Gibraltar's waters.
The Foreign Office said it had demanded a meeting with ambassador Federico Trillo, in the last twist to a diplomatic row over the territory in the southern Iberian peninsula that has been escalating in recent months.
"Despite repeated diplomatic protests to Spain in relation to incursions into British Gibraltar territorial waters in recent months, a Spanish state research vessel, the RV Ramon Margalef, undertook significant surveying activityon 18 and 19 November for over 20 hours," the minister for Europe, David Lidington, said.
"When challenged, the vessel responded that it was conducting survey work with the permission of the Spanish authorities and in the interests of the European Community."
Lidington said the incident was the latest in a series of similar breaches of British territorial waters by Spanish ships.
"This comes only two weeks after dangerous manoeuvres by a Spanish Guardia Civil vessel in the vicinity of Royal Navy vessels in British waters put lives at risk and resulted in a minor collision," Lidington said.
"I strongly condemn this provocative incursion and urge the Spanish government to ensure that it is not repeated. We stand ready to do whatever is required to protect Gibraltar's sovereignty, economy and security."
Diplomatic tension between London and Madrid has been growing since Gibraltar built an artificial reef in disputed waters. According to Spain, the reef has damaged the livelihood of local fishermen and the environment.