Nine people were injured and a truck was set on fire, after students from the school where 43 trainee teachers went missing last year clashed with the police on the outskirts of Chilpancingo on 22 September, local media reported. The one-year anniversary of the disappearance is days away.

The clashes started around 7.40am when a group of students and relatives headed from Tixtla, where the school is located, to Chilpancingo to take part in a protest. At a checkpoint, set-up by state officers with the deployment of riot policemen on the Tixtla-Chilpancingo highway, at the entrance to a tunnel along the highway, the students allegedly refused to allow the police on board buses carrying the protesters.

Some hooded students, got down from the buses to talk to the police, asking them to let them through. When the police refused to do so, all the students descended from the buses, placed a truck across the tunnel and set fire to it, local media reported. The students then reportedly threw rocks, molotov cocktails and rockets at the police, who responded with tear gas to try to disperse them.

"These people, in an aggressive way, with tear gas (canisters), some homemade rockets attacked the state forces during a routine check-up," said Guerrero State Public Security Minister, Pedro Almazan.

Seven Guerrero state police officers and two students were injured in the clashes, which lasted about half an hour, local media reported. Four police officers - including two female officers - were held hostage until 10.30am when they were released and sent back to Chilpancingo on board ambulances, according to local sources.

Local media reported that federal and state authorities have set-up checkpoints on highways leading into the capital city Chilpancingo, to avoid violent protests as one the year anniversary of the students' death, on 26 September approaches.