Citigroup Inc. (C), one of the world's largest financial services companies, on Wednesday said it plans to launch its own electronic stock-trading network, a service that could draw some traffic away from the New York Stock Exchange and Nasdaq Stock Market.

The exchange — also known as an electronic communications network, or ECN — would be built around Citigroup's recent acquisition of OnTrade Inc. , an ECN operated by NexTrade Holdings Inc.

The OnTrade ECN will continue to operate in its current state while its new owner performs some technology enhancements, Citigroup said, and the new ECN could be ready to begin processing trades in the second quarter.

The move comes as the two largest U.S. stock exchanges begin to expand electronic trading through acquisitions. The NYSE plans to transition into a for-profit company to be named NYSE Group Inc. through its acquisition of Archipelago Holdings Inc. , a deal expected to close later this month or in early February. Meanwhile, the Nasdaq Stock Market snapped up Instinet from Reuters.

"In a time of significant changes in market structure, our goal is to create an ECN that provides execution flexibility for ourselves, other broker/dealers, and our respective clients," said Jim O'Donnell, head U.S. equities at Citigroup.

There has been some speculation that the stock exchanges might consider raising fees to broker/dealers after making their respective acquisitions. The new venture would allow Citigroup to buy and sell stocks in-house, and the network could be opened up to other brokerages.

James Forese, head of Citigroup Global Equities, said the company expects the new exchange will increase market efficiencies, deliver best execution, and reduce transaction costs.