Investors in Satyam Computer Services Ltd's American Depositary Receipts (ADRs) have filed two class action suits against the Indian software services firm, the law firms representing the investors said on Thursday.

Vianale & Vianale LLP and Izard Noble LLP have filed suits alleging Satyam and its top executives violated federal securities laws by issuing false and misleading financial statements, the law firms said in separate releases.

On Wednesday, Satyam's founder and chairman Ramalinga Raju resigned and said profits had been falsely inflated for years, sending the company's shares down 80 percent in Mumbai.

Trading in Satyam's ADRs was suspended before the opening of U.S. trade on Wednesday

Izard has filed a lawsuit in the United States District Court for the Southern District of New York, while Vianale's suit is pending in the Manhattan federal court.