Three Swiss bankers accused of conspiring with American clients to hide more than $420 million from the tax-collecting U.S. Internal Revenue Service were indicted, the U.S. Attorney's Office in Manhattan said on Wednesday.

The indictment named Stephan Fellmann, Otto Huppi and Christof Reist, all former client advisers with an unnamed Swiss bank. None of the bankers have been arrested, authorities said.

Their attorneys were not immediately known.

The indictment said the unnamed bank did not have offices in the United States.

Banking secrecy is enshrined in Swiss law and tradition, but it has recently come under pressure as the United States and other nations have moved aggressively to tighten tax law enforcement and demanded more openness and cooperation.

In April, two Swiss financial advisers were indicted on U.S. charges of conspiring to help Americans hide $267 million in secret bank accounts.

In January, prosecutors charged three Swiss bankers with conspiring with wealthy taxpayers to hide more than $1.2 billion in assets from tax authorities.

UBS AG, the largest Swiss bank, in 2009 paid a $780 million fine as part of a settlement with U.S. authorities who charged the bank helped thousands of wealthy Americans hide billions of dollars in assets in secret Swiss accounts.