Swiss bank ZKB said on Thursday that two of its bankers and one former banker had been indicted by U.S. authorities on charged they helped U.S. clients to cheat on their taxes.

The U.S. Attorney's Office in Manhattan announced charges on Wednesday against three Swiss bankers, who the government said conspired with U.S. clients to hide more than $420 million from the Internal Revenue Service.

ZKB said in a statement it was cooperating with U.S. authorities. The bank said it could give no details about the employees due to the ongoing investigation.

Switzerland's cherished bank secrecy has come under pressure in recent years as the United States and other nations move aggressively to tighten tax law enforcement and demanded more openness and cooperation.

(Reporting by Caroline Copley)