A 15-year-old boy lost his hand when he clashed with riot police during an education protest in Lens, northern France, on Monday. Police are investigating what happened.

The teenager lost his hand and part of his lower arm after picking up a police dispersal grenade that exploded, the regional newspaper La Voix du Nord reported. The boy’s life is not in danger.

Police prefect Francois-Xavier Lauch declined to comment on the exact circumstances. He said 200 to 250 protesters had been hurling objects at police, who intervened. The General Inspection of the National Police will lead an internal investigation.

The protests began on September 17 at a high school in Creteil, a Paris suburb, over understaffed and crumbling schools. The movement has spread nationwide. About 500 schools closed on Monday. Around 5,000 people, mostly teenagers, have been arrested since the protests began.

On Tuesday, students blocked schools from Lille to Marseille as trade unions held street protests. Prime Minister Sebastien Lecornu has ordered ministers to answer the students’ demands, including replacing absent teachers and repairing old buildings.