Brussels - Belgian police arrested 11 people in anti-terrorism raids targeting jihadists who have returned from Syria, prosecutors said on Wednesday.Police raided nine houses in various areas of Brussels including Molenbeek, the district that was home to several of those involved in the Paris and Brussels attacks."The investigation was launched in relation to the issue of possible returning Syria fighters," the federal prosector's office said in a statement in English."In all, eleven persons were arrested and taken for questioning."No weapons or explosives were found, the prosecutor said."This case is completely independent from the case files concerning the attacks in Paris of 13 November 2015 or in Brussels/Zaventem of 22 March 2016," the statement added.Belgium has been on high alert since three suicide bombers attacked Zaventem Airport and the Brussels metro system in March 2016, killing 32 people.Several people have been jailed in Belgium in recent years for recruiting jihadists to fight for the Islamic State group in Syria.Prosecutors said earlier on Wednesday that one of them, Khaled Khattab, a friend of Brussels airport bomber Najim Laachraoui, managed to flee Belgium last year despite having been sentenced to seven years in prison for involvement in a recruiting network.