The protests were held Thursday as the new law took effect, although without its strongest provisions.
Phoenix police say they arrested 45 people during protests in front of Maricopa County Sheriff Joe Arpaio's headquarters downtown and in surrounding areas.
The Maricopa County Sheriff's Office arrested 23 people outside a downtown jail where protesters beat on the metal door and forced sheriff's deputies to call for backup. Officers in riot gear opened the doors, waded out into the crowd and hauled off those who didn't move.
The U.S. Marshals Service arrested three people in front of the federal courthouse downtown.
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