Demonstrators have clashed with police in Mexico's capital in a massive march protesting President Enrique Pena Nieto's handling of the apparent massacre of 43 college students.
The skirmishes outside Mexico City's National Palace Thursday marred a mostly peaceful rally attended by thousands of people.
Earlier Thursday, masked demonstrators sparred with police near Mexico City's airport, throwing Molotov cocktails and fireworks.
The students vanished on September 26 in the city of Iguala. Officials believe the students were rounded up by local police and turned over to a local drug gang, Guerreros Unidos. The gang allegedly killed the students, burned their bodies and threw the ashes into a river.
The students' parents have rejected claims their children are dead and have demanded the government find them alive.
Dozens of people have been arrested in connection with the kidnapping, including members of the Guerrors Unidos gang, more than two dozen police officers and the ousted mayor of the city of Iguala and his wife.
Authorities say Mayor Jose Luis Abarca ordered the officers to confront the students over fears they would derail a speech by his wife, who headed the local child protection agency.
The crime has infuriated Mexicans fed up with corruption, impunity and a drug war that has left tens of thousands of people dead or missing.