German police have carried out raids across Berlin on properties linked to a mosque used by the Christmas market truck attacker, Anis Amri.
Fifteen apartments and two commercial premises were searched in the city in an operation involving 460 police. Six prison cells were also searched.
The organisation which ran the mosque has been closed down.
Twelve people were killed and more than 50 injured by Amri, a Tunisian asylum seeker, in December.
He was shot dead by police after fleeing to Italy.
Police say the raids follow a decision to ban the organisation, known as Fussilet 33, in mid-February. The properties targeted were used by those who ran the organisation, police said.
German prosecutors say that Amri visited the mosque frequently, including on the day of the attack.
Police suspect it was a centre for radicalising Muslim recruits for so-called Islamic State in Syria and collecting funds for IS attacks.
Police kept watch on the building with a camera positioned opposite the entrance. The mosque closed down a week ago.
Berlin State Interior Minister Andreas Geisel told a news conference that more apartments were raided in the state of Brandenburg and the city of Hamburg.
Leading figures in Fussilet 33 were already in prison while being investigated on allegations of supporting terrorism abroad or preparing acts of terrorism, he said. These included former imams of the mosque and members of the organisation's board.
"With this strike against Islamist terrorism, Berlin is sending a clear signal that people who act against our free democratic basic order, people who are committing violent acts or preaching violence don't have a place in this city," Mr Geisel said.
Amri carried out his attack on 19 December at the market in central Berlin. He hijacked the lorry after killing its Polish driver before ploughing through the stalls, killing 11 people.