ZURICH-- Credit Suisse AG said on Thursday that regulators have asked it for information about its alternative trading platform as a probe into high-frequency trading and "dark pool" trading venues expands.

Zurich-based Credit Suisse said it was cooperating with "various governmental and regulatory authorities" regarding its alternative trading systems.

The bank gave no more details about who is conducting the investigations.

Switzerland's second-largest bank by assets also said it is among 30 defendants named in lawsuits filed with the U.S. District Court for the Southern District of New York. The complaints are related to alleged violations of U.S. securities laws related to high-frequency trading, the bank said.

Earlier in the week, UBS AG and Deutsche Bank AG said they were cooperating with authorities investigating so-called dark pools which are securities markets that allow investors to buy and sell shares in an anonymous manner to hide their trading activity from rivals.

Last month, New York Attorney General Eric Schneiderman filed a lawsuit alleging that Barclays PLC favored high-frequency traders in its dark pool and misled other clients about their participation. Barclays has contested the claim.

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