German police staged raids on the DWS unit of Deutsche Bank in Frankfurt, the state prosecutor's office said on Tuesday, giving no further details.
DWS said it has continuously cooperated with regulators and authorities and would continue to do so.
No one at Deutsche Bank was immediately available to comment.
Handelsblatt business daily first reported the raid.
According to Handelsblatt, the raid by around 50 officials on Deutsche Bank's Frankfurt headquarters and the nearby building housing the DWS Group was over green-washing allegations against the latter.
The U.S. Securities and Exchange Commission as well as Germany's financial regulator BaFin have separate investigations into allegations that DWS overstated how it used sustainable investing criteria to manage investments.
DWS has denied those allegations.
Fund managers have rapidly amassed billions of dollars of assets that are meant to have an environmental or social profile, but there is growing scrutiny over how firms define and apply environmental, social and governance (ESG) standards.