Spanish police say they have dismantled a clandestine casino in Madrid where illegal gambling tournaments allegedly took place concealed behind the facade of an establishment purporting to be a smoking club.

Investigators received tip-offs from legitimate casinos and began surveillance on an underground location in downtown Madrid where people were received by porters.

Once inside the building, the alleged gamblers — who needed to arrive with an invitation — were escorted through two security doors equipped with an airlock and down to gaming rooms.

One had eight card-game tables while the other had two and was reserved for "VIP gamblers" attended by hostesses.

Police said Thursday that they identified 100 people, and seized cash and equipment, when they raided the establishment, without specifying when the operation took place.