Thousands of Mexicans have been marching through the streets of Mexico City to protest against the pace of investigations on the whereabouts of 43 missing student teachers.
They disappeared after clashing with police in the south-western state of Guerrero more than five weeks ago.
University students have begun a 72-hour strike in support of the teachers.
The mayor of Iguala, suspected of involvement in their disappearance, was arrested on Tuesday after a manhunt.
Jose Luis Abarca and his wife were detained without a shot being fired in a house in a working-class neighbourhood of Mexico City.
A woman who had rented the house to the couple was also arrested on suspicion of aiding a fugitive.
The nationwide strike is the latest in a series of protests aimed at putting pressure on the authorities to step up the search for the missing students from a teacher-training college in the town of Ayotzinapa.