CHICAGO (CBS) — Chicago Police say 121 immigration rights demonstrators were arrested at a sit-in on Clark Street at Congress this afternoon.

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Police say the demonstrators blocked traffic on Clark Street for almost an hour. The police line on Congress blocked one lane of traffic on the south side of the street, police say.

The U.S. Citizenship and Immigration Services building at 101 West Congress Parkway was the focus of the demonstration.

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Organizers say they want Congress to approve immigration reform.

At least 200 people took part, including some Chicago aldermen.

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Police say the arrests were made without incident.