Spanish police say they have freed eight women who were being held at a house in Marbella, and arrested 21 presumed members of a gang that allegedly sexually exploited them.

Police said in a statement Sunday the women were prevented from leaving the basement of the house where they worked as prostitutes. They were subjected by the gang to "exhausting long days, fines and threats."

Some of the captive women were recruited to work as prostitutes but others had been told they would be working at a massage parlor in the southern Spanish city.

Police believe the arrested suspects were part of a Portuguese-led gang that also sold drugs.

Authorities acted on a tip-off to a police hotline for cases of sexual exploitation.