Gibraltar/Madrid  - Britain's Princess Anne on Thursday inaugurated a military hospital in the British overseas territory of Gibraltar in an act that irritated Spain, Spanish media reported.

The hospital was located in a border area the sovereignty over which was unclear, Jose Carracao of Prime Minister Jose Luis Rodriguez Zapatero's Socialist Party was quoted as saying.

Already in January, Spain protested to the British embassy in Madrid about the royal visit, describing it as "inopportune."

The visit could "hurt feelings" in Spain, which claims sovereignty over Gibraltar, senior official Angel Lossada told ambassador Denise Holt.

However, the diplomatic protest was coined in the mildest possible terms, according to the daily El Pais.

Jose Ignacio Landaluce of the opposition conservative People's Party called Princess Anne's trip to Gibraltar a "provocation."

The outpost of 30,000 residents was ceded to Britain in the 1713 Treaty of Utrecht. (dpa)