Students and relatives of 43 missing aspiring teachers stormed a Mexican military base on Monday in the city where they vanished, prompting soldiers to repel them with tear gas.
The protesters traveled to Iguala, in the southern state of Guerrero, to demand to search the barracks because they believe the missing young men may have been hidden there.
When the soldiers refused to let them in, the group hijacked a soda company's truck and used it to break through a gate, but soldiers and police stopped them from going further than 20 meters (yards).
Protesters threw empty beer bottles taken from another truck. Four people were lightly injured.
Authorities say the 43 young men were abducted by Iguala police officers on September 26 and delivered to the Guerreros Unidos drug gang, whose henchmen confessed to killing them.
Only one student has been identified among charred remains found near Iguala, and relatives of the young men refuse to believe they all died.
For weeks, parents of the students have said that they suspect that soldiers played a role in the events that led to their disappearance.
"I am really mad because we came peacefully to ask military authorities to let us go in to look for our sons because were were told that they could be there," Mario Gonzalez, father of a missing student, told AFP.