Madrid - Spain on Friday protested to London over an incident off the disputed British enclave of Gibraltar, where a British navy patrol vessel practiced shooting at a buoy painted with the colours of the Spanish flag.

Spain's foreign ministry said a senior ministry official met with British ambassador Giles Paxman, who apologized for the incident, saying the buoy did not intentionally carry Spanish colours.

Britain promised to investigate the incident, the ministry said.

The daily El Mundo said a Spanish police patrol boat saw the crew of a British navy patrol vessel pick up a buoy it had been shooting at earlier this week.

Spain's conservative opposition has asked Foreign Minister Miguel Angel Moratinos to explain why Madrid had not taken stronger action against what the opposition regards as British pressure to make Spain renounce its claim of sovereignty over the enclave of 6.5 square kilometres.

Gibraltar, which has about 30,000 residents, was ceded to Britain by the 1713 Treaty of Utrecht. (dpa)