The alert status for Brussels was raised to the highest level on Saturday, shutting the metro and warning the public to avoid crowds because of a "serious and imminent" threat of an attack. A week after the Paris assault by Islamic State terrorists, of whom one suspect from Brussels, Salah Abdeleslam, is at large and highly dangerous, the city was placed on the top, fourth level of Belgium’s threat scale, although the cause of the alert was not disclosed. Belgian authorities conducted nine raids Thursday in several parts of Brussels. Nine people were arrested. One person who has not yet been identified was charged.