A British warship set sail for the Mediterranean on Tuesday (August 13) amid diplomatic tensions between Britain and Spain over the contested British overseas territory of Gibraltar.

The HMS Westminster, a type 23 frigate, will dock in Gibraltar as part of a Royal Naval deployment of 10 vessels, called Cougar '13, to the Mediterranean and Gulf.

On completion of the exercise in Gibraltar, HMS Westminster will deploy to the Middle East and Indian Ocean, the Royal Navy says.

The departure of the ship from Portsmouth, played down by the British and Spanish governments as part of a long planned, routine exercise, has underscored heightened tensions over the territory.

A helicopter carrier, HMS Illustrious, also left Portsmouth for Gibraltar on Monday (August 12).

Britain has warned Spain it might take legal action to try to force Madrid to abandon tighter controls at the border with Gibraltar in what it called an "unprecedented" step against a European ally.

Opposition politicians in Spain have accused Prime Minister Mariano Rajoy of using the situation to distract Spaniards from the country's severe recession and a corruption scandal.

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