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Seventeen people, including children, have been "rescued" as part of a human trafficking investigation.
West Yorkshire Police said the people, mostly from Slovakia, were taken from 25 different addresses in south and west Leeds.
The force said the three-day-operation was part of an investigation into an "organised criminal gang" thought to be involved in human trafficking, benefit fraud and labour exploitation.
During the operation police officers worked with council staff and charity workers to visit 25 properties where families had been "identified as being potential victims of trafficking".
Most of the 17 people taken into police care and put into the National Referral Mechanism are from Slovakia, police said.
Another 33 people "preferred not to co-operate and remained where they were".
Det Ch Insp Andy Williams said: "A multi-agency operation on this scale involving such a large number of potential human trafficking victims is unprecedented in West Yorkshire.
"Many were living in very poor housing conditions with no access to local support services and little if any income to exist on. Others were having their benefits taken from them and being exploited by being forced to work long hours for little or no pay."
Maj Anne Read from the Salvation Army, which was involved in the operation, said it was working with West Yorkshire Police to support the victims.
She said: "Our team has been working to assess the needs of the victims and ensure that they have access to accommodation and support at safe houses if needed."
Mr Williams said the investigation was ongoing and further arrests were expected.