NEW YORK, May 6 (Reuters) - The biggest intraday point drop ever in the Dow Jones Industrial Average may have been caused by an erroneous trade entered by a person at a big Wall Street bank, multiple market sources said on Thursday.

The so-called “fat finger” trade apparently involved an exchange-traded fund that holds shares of some of the biggest and most widely traded stocks, sources said. The trade apparently was put in on the Nasdaq Stock Market, sources said.

Several sources said the speculation is that the trade was entered by someone at Citigroup C.N. A Citigroup spokesman said it was investigating the rumor but that the bank currently had no evidence that an erroneous trade had been made. (Reporting by Matthew Goldstein; Editing by Gary Hill)