The German stock market watchdog has begun an inquiry into Deutsche Bank over its role in the sale of about 44 million shares in Deutsche Telekom. The sale, executed on behalf of several Deutsche Bank customers on Tuesday, led to a sharp drop in the price of Deutsche Telekom shares, which fell to the lowest level in nearly three years.

Just a day earlier, Deutsche Bank had reiterated its "buy" recommendation on the stock. "We are very disappointed by the conduct of Deutsche Bank, with which we have until now maintained good business relations," a Telekom spokesman said.