German officials have voiced concern over the possibility of thousands of former Taliban fighters having entered Germany over the past two years among an influx of more than a million migrants and refugees, Der Spiegel magazine reported on Saturday.

Germany’s Federal Office for Migration and Refugees (BAMF) informed security officials that thousands of migrants had identified themselves as former Taliban insurgents during the asylum application process, the magazine said.

It stated that at least 70 Afghan men were being investigated by Germany’s over-stretched chief federal prosecutor, though it was not clear whether all of them were suspected of being active Taliban militants.

According to the magazine, six are being held in detention and preliminary court hearings involving several others are due to start next week.

No comment was immediately available from the migration office or federal prosecutors.

The German government has recently come under fire for allowing in so many migrants, especially after several militant attacks were linked to migrants last year. Germany has however been deporting groups of rejected Afghan asylum seekers in recent months.