Mexican police officers were captured on camera throwing rocks at a bus carrying student protesters from the institute attended by 43 trainee teachers who went missing last autumn.
The incident happened last weekend in Chilpancingo, a district of the violence-ridden southern state of Guerrero.
Riot police halted a coach carrying about 50 trainee teachers from the Rural Normal School of Ayotzinapa, as it was traveling on a federal road connecting Chilpancingo to Iguala, a city that became infamous worldwide as the site of the disappearance and murder of 43 students from the same school.
Local media reported the bus initially failed to stop at a checkpoint set up over the alleged theft of a gas pipe. Footage recorded by the local Guerrero News Agency shows the officers in riot gear surrounding the vehicle and attempting to force the students out.
As the trainee teachers refuse to open the front door, several policemen hurl rocks at vehicle, smashing its windows. Security forces then fire tear gas, eventually getting the protesters off the bus. Several students and police officers were reportedly injured in the clashes that ensued.
The incident came just two days after a few thousand demonstrators rallied in Mexico City to mark the six-month anniversary of the disappearance of the 43 Ayotzinapa students.
According to federal prosecutors, they were held by corrupt officials during a demonstration in Iguala upon the orders of the city's mayor and his wife and then handed over to a local drug gang, the Guerreros Unidos.
They were subsequently murdered and their bodies burned on a pyre for 14 hours making it almost impossible for authorities to identify the remains, authorities said.
The Rural Normal School is considered a hotbed of unrest, with its left-leaning students, who come from rural and impoverished Guerrero communities, having a long history of participating in anti-government protests.
The missing students had gone to Iguala to collect money and hijack buses to be used to drive to other events in Mexico City, AP reported.