Citadel Securities plans to shut down its Apogee “dark pool” in the US, according to people familiar with the matter, as the US market maker focuses on its faster-growing off-exchange trading platform aimed at institutional investors.

Details on when the shutdown will occur couldn't be learned. The move comes as competition among dark pools and operators of other private trading venues is set to intensify. In January, Nasdaq OMX Group said it had approached several large banks to take over their dark pools. That same month, The Wall Street Journal reported that a group of money managers led by Fidelity Investments was close to launching a private trading venue.