(The Wall Street Journal) -- A criminal probe into potential securities-law violations at German bank WestLB has widened to include seven current and former board members, including former chief executive Thomas Fischer, according to a local prosecutor. The move deals a blow to the bank's efforts to explore sale or merger options.

The probe stems from an investigation into trading activities at WestLB's proprietary desk. The inquiry began in April after the bank disclosed that its traders lost €70m ($95.3m) in the first quarter, kicking off a criminal investigation of two of the traders.