A German exchange student is recovering in hospital from wounds sustained when police fired on the vehicle in which he was travelling through southern Mexico with a group of friends. The group, who were returning to Mexico City after a weekend at the beach resort city of Acapulco, included another student from Germany and others from France and Mexico, according to local media.

The incident took place on Sunday night on the Motorway of the Sun, linking Acapulco to the capital, near the city of Chilpancingo in the state of Guerrero, where police and unidentified gunmen attacked trainee teachers on 26 September. That attack, in the city of Iguala, left six people dead and 43 students missing. They have not been found, though 26 officers from Iguala have been detained and officials are attempting to determine if any of the students are in 10 newly discovered mass graves.

The state has a severe security crisis and has been blighted by the widespread collusion of its police forces with organised crime, which has added to the distrust of law enforcement officers.

Sunday’s shooting has been officially blamed on police confusion, with possible violations of rules defining when opening fire is justified.

A statement released by the state prosecution office said the police had set up checkpoints along the roads around Chilpancingo following an earlier incident in which a member of the state anti-kidnapping unit was shot dead.

The statement said that the van in which the students were driving had failed to stop when ordered. “Immediately after, there was a sound similar to a detonation and some of the officers opened fire, wounding one of the passengers in the van.”

Victor León Maldonado, the deputy attorney general, told reporters that the officers had aimed low in an effort to blow out the vehicle’s tyres. The wounded German student was shot in the buttocks, he said.

Maldonado said that the 15 to 20 police officers involved in the incident had been detained. Travellers had an obligation to obey police orders to stop, he said, but the failure to do so should not mean they are shot at.

The director of the wounded German student’s university, the Monterrey Institute of Technology, told the newspaper El Universal that the 25-year-old was in a stable condition in a Mexico City hospital and should be discharged in a few days’ time. He began an exchange programme in business studies in August.