MARSEILLE, France—Police in the French city of Marseille detained a man Friday who was wielding a knife outside a Jewish school and kosher market. Surveillance of Jewish sites in the city has been increased while they investigate his motives, according to local authorities. School security guards noticed the man visibly brandishing a knife outside the Yavne School and then trying to enter a kosher market nearby, where they detained him, a Marseille police spokeswoman told The Associated Press. The children were briefly sequestered inside the school while police searched for any explosives or accomplices, she said. No one was hurt in the incident and the man’s motives remain unclear, she said. The spokeswoman was not authorized to be publicly named. Police towed away the suspect’s car and cordoned off the area. A witness said it was a rapid police operation, and described the area as a gathering place for people …