Spain's Civil Guard police force on Tuesday searched the headquarters of Catalonia's regional police, the Mossos d'Esquadra, in a probe centred around the outlawed independence referendum on October 1, a spokesman said.

"We're carrying out an inspection related to the Mossos d'Esquadra's communications on the day of the illegal referendum on October 1," the Civil Guard spokesman told AFP, adding officers were searching the headquarters in Sabadell, a city in Catalonia, and other offices.