BERLIN - Police launched dawn raids across Germany on Tuesday on about 190 mosques, flats and offices linked to an Islamist group after the government banned the organisation, accusing it of radicalising youngsters.

Interior Minister Thomas de Maiziere said the DWR 'True Religion' group had persuaded about 140 people to join militants in Iraq and Syria.

DWR, also known as "READ!" made no reference to the raids on its website and did not immediately respond to a request for comment. De Maiziere said it had several hundred members.

Pictures showed masked police officers carrying away computers and files from properties. Chancellor Angela Merkel has come under pressure to harden her line on security after several attacks claimed by Islamic State across Europe, including a bombing and a knifing in Germany that wounded some 20 people in July. She is also under fire for letting in about 900,000 migrants, mostly Muslims, last year.

Last month, a Syrian committed suicide in prison after he was arrested on suspicion of planning to bomb an airport.

His brother and friends have said he was "brainwashed" by ultra-conservatives imams in Berlin.

The domestic intelligence agency said in June about 8,900 ultra-conservative Islamists known as Salafists were in Germany.

De Maiziere said Tuesday's raids in 10 German states were the biggest crackdown on any group since the government shut down a movement known as Kalifatstaat (Caliphate State) in 2001, accusing it of extremist activities.