Many of the suspected extremists have been captivated by Islamic State propaganda, Georges Oswald, a deputy public prosecutor, said in an interview with RTL on Monday.

All 11 were already on counter-terrorism unit’s “radar”, he told the broadcaster. Six are believed to have gone to fight in Syria, some of whom have possibly been killed.

The total number of alleged radicals tracked by Luxembourg police has risen compared to before the Syrian war, but the figures have remained more or less stable in recent months, Oswald stated on 24 July.

In addition to the tipline, the counter-terrorism squad is working with school and prison authorities on prevention programmes.

Earlier this month, a separate outfit launched, called Respect.lu, that also combats radicalisation.