German police have searched a mosque and eight apartments in Hildesheim that are believed to be a hotbed of a radical Salafist community, the interior minister of the northern state of Lower Saxony said on Thursday.

Germany is on high alert after a spate of attacks since July 18 left 15 people dead — including four attackers — and dozens injured. Two assailants, a Syrian asylum seeker and a refugee from either Pakistan or Afghanistan, had links to Islamist militancy, officials say.

Interior Minister Boris Pistorius said in a statement that up to 400 police — including mobile squads and a special forces police commando — were involved in the raids on Wednesday in the Hildesheim area, which is a short drive south of Hanover.