During a major raid against money laundering and organized crime, the police searched apartments and offices in North Rhine-Westphalia, Lower Saxony and Bremen on Wednesday morning and carried out ten arrest warrants.
More than a thousand police forces are in use, including special units, the police said in the morning.
The investigations were directed against members of an international money laundering network.
The aim is to seize evidence and illegal assets.
The public prosecutor's office in Düsseldorf wanted to announce more details at a press conference in the afternoon.
"The operation is still running," said a spokesman in the morning.
According to the report, a central office for the prosecution of organized crime at the Düsseldorf public prosecutor is conducting the investigations, which are directed against members of a so-called hawala network.
With hawala banking, customers can transfer large sums abroad for a commission.
Such financial transfers are only allowed in Germany with the approval of the banking supervisory authority. 80 houses, apartments, offices and business properties were searched. The arrest warrants against ten suspects were obtained in advance and carried out on Wednesday, the statement said.
According to WDR information, the alleged money smugglers are said to have transferred more than 100 million euros from illegal transactions to Turkey and Syria.
The money comes from drug trafficking, among other things, and is said to have been used in part to finance terrorism in Syria.
The starting point of the investigation was a chance find by the police.
The officers found 300,000 euros of cash hidden in a gym bag during a check on the autobahn, reported the WDR.
The police spokesman did not want to comment on the background to the operation and referred to the press conference in the afternoon.