Protesters marched in several cities in Mexico on Monday to mark the second anniversary of President Enrique Pena Nieto's administration and demand the government find 43 students who disappeared at the hands of police.
In Chilpancingo, the capital of the southern state of Guerrero, demonstrators attacked the state prosecutor's office, torching several vehicles outside and breaking windows and office equipment.
An official of Mexico's Pemex oil company said protesters led by a teachers' union also blockaded roads leading to a state-owned oil refinery in the southern state of Oaxaca, preventing traffic from entering or exiting.
The official, who was not authorized to be quoted by name, said the demonstrators had not entered the refinery in the township of Santa Maria El Tule, and the facility did not shut down.
Thousands more marched along a main avenue in Mexico City, led by a small group of parents of the 43 missing students.
The students were detained in the city of Iguala, Guerrero, by local police in September. Prosecutors say they were handed over to members of a drug gang who reportedly killed them and incinerated their remains.
Two new polls published Monday showed Pena Nieto's approval ratings falling to around 40 percent, some of the lowest levels for a Mexican president since the economic crisis of 1994-1995.