German authorities say three people have been arrested in raids conducted as part of efforts to root out people sent to Europe by the Islamic State group or other extremists amid the migrant influx.

The Federal Criminal Police Office said six locations in two German states were searched Tuesday. It said three people were detained and "extensive material" seized, but didn't give more details. The raids were first reported by the daily Die Welt.

The office noted that the attacks in Paris and Brussels over the past year showed that IS has used the migrant flow to send people to Europe. It said it's received over 400 tips about people who may have a terrorist background, but most turned out to be wrong. However, more than 60 investigations were opened.