Securities and futures regulators said late Thursday they were working with exchanges to examine "unusual" trading activity during the day's massive sell-off, which saw bellwethers such as Procter & Gamble Co. plunge nearly 40%, and prompted a senator to call for tighter trading controls.

The U.S. Commodity Futures Trading Commission and the U.S. Securities & Exchange Commission said in a joint statement late Thursday that they are working closely with other financial regulators and exchanges "to review the unusual trading activity that took place briefly this afternoon."

The regulators said they would make the findings of their review public. (read more at marketwatch.com)