The British Foreign Office is set to make a formal protest to Spain after a Spanish navy ship was found to have entered what Britain describes as British territorial waters around Gibraltar earlier this week, local media reported Wednesday. "There was an incursion into British waters near Gibraltar by the Spanish navy on 18 February, during a Royal Navy exercise. We are raising this at a high level with the Spanish government and will be issuing a formal protest," a British Foreign Office spokesman was quoted by local media as saying. British military chiefs temporarily suspended the training exercise as a result of the incursion, according to a BBC report. Gibraltar, located on the southern tip of the Iberian Peninsula at the entrance of the Mediterranean, was ceded to Britain as part of the Treaty of Utrecht in 1713, but Spain has persistently sought to regain the tiny southern territory. Last year, Gibraltar authorities dropped tens of concrete blocks in the Bay of Algeciras to form an artificial reef, which Spain said had blocked its fishermen. Spanish police and civil guards responded by tightening border controls, causing long delays for those crossing the border.