GENEVA - The United States Justice Department is investigating whether Credit Suisse Group helped wealthy American clients evade taxes by keeping money in secret accounts, the Swiss bank said Friday.

The investigation is part of a wider probe into the role banks played in facilitating tax evasion by U.S. citizens.

Credit Suisse is the highest profile Swiss bank to be targeted since rival UBS AG admitted three years ago to helping U.S. clients hide money in offshore accounts in Switzerland and elsewhere. It ended up paying a $780 million fine and giving U.S. authorities details on thousands of American account holders.

The case prompted Switzerland to soften its strict banking secrecy rules by agreeing to provide more information to foreign authorities investigating alleged tax evasion.

Credit Suisse said it was informed of the investigation by letter Thursday and will cooperate with U.S. authorities within the limits set by Swiss banking secrecy laws.

The bank stopped providing cross-border private banking services to Americans in 2008.

Switzerland's top court on Friday upheld the Swiss government's right to order the handover of UBS customer data, a move that was challenged by some of the affected clients. The Federal Tribunal in Lausanne said the government had the right to use emergency powers to prevent "serious and virtually uncontrollable economic repercussions for Switzerland" had it failed to order the release of the files.

Observers had expected a formal investigation against Credit Suisse after three former and one current employee of the bank were indicted by U.S. authorities in February on charges of conspiring to help American tax cheats.

Analysts at Zuercher Kantonalbank noted that a new treaty currently being discussed by Bern and Washington - which would automatically tax the accounts of American bank clients in Switzerland - might ease the pressure on Credit Suisse and other Swiss banks.

A spokesman at the Swiss Finance Department, Mario Tuor, told The Associated Press last month that the aim of the talks was to reach a "comprehensive solution" that would cover all past tax infringements by U.S. clients and Swiss banks.

Tax experts say Switzerland has few trumps left to play while U.S. authorities are accumulating piles of evidence against Swiss banks from voluntary disclosures by U.S. clients seeking reduced punishment for tax evasion.

"What the Swiss are trying to do is just get this whole thing resolved," said Milan K. Patel, a Zurich-based tax lawyer. If they fail to reach an agreement, Swiss banks could lose their license to operate in the U.S. and senior employees could face prosecution, he said.

Shares in Credit Suisse, which releases its second-quarter results July 28, closed 1.5 percent lower at 30.12 Swiss francs ($36.91) on the Zurich exchange.