The FBI said on Monday it was probing high-speed trading on Wall Street, a controversial practice in which computers carry out transactions in seconds or faster.
Investigators are looking into possible securities fraud, wire fraud and insider trading by companies or people who engage in this kind of trading based on rapid fire transactions using complex algorithms, an FBI spokesman told AFP.
The official would not say if the probe is being carried out in conjunction with an investigation by New York State Attorney General Eric Schneiderman.
The attorney general for months has been probing high speed traders, which he says are a potential source of unfair competition by allowing traders split-second advantages over rivals.
Scheiderman's office confirmed in mid-March a probe was underway.
Debate on high-speed traders was renewed Monday with the release of the book "Flash Boys: a Wall Street Revolt" by Michael Lewis.
Lewis argues that the New York bourse is plagued with traders who profit time-wise from ultra sophisticated technologies that other investors cannot match.