France will mobilize up to 7,000 soldiers to increase security around the country after a teacher was fatally stabbed and three other people wounded in a school attack by a former student suspected of Islamic radicalization, the president’s office said Saturday.

Some schoolchildren, parents and personnel returned to the Gambetta-Carnot school in the northern city of Arras as it reopened Saturday morning to reconnect and seek support, after the attack Friday that rattled France in a context of global tensions over the Israel-Hamas war.

Counterterrorism authorities are investigating the stabbing, and the suspected assailant and several others are in custody, prosecutors said. The suspect had been under recent surveillance by intelligence services for radicalization. Court documents viewed by The Associated Press show he is from the Ingushetia region in Russia’s Caucasus Mountains, which neighbors Chechnya. Authorities had initially identified him as Chechen.