Rajoy promised "legal and proportional steps," the British newspaper The Daily Telegraph reported. He gave a news conference a day after the British government announced the deployment of a group of nine ships to Gibraltar, including three that will dock there.
The 2.6-square-mile promontory off southern Spain has been British territory since 1713. Gibraltar has become a major bone of contention between the two countries.
The current row began with a dispute about fishing when Spain objected to the construction of a breakwater. Britain said the structure is needed to restore fish stocks depleted by Spanish fishermen.
Britain said the deployment of the naval force has been planned for a long time and is a normal part of its military operations. But the announcement was made Thursday after days of rising tension.