Banking giant Credit Suisse "helped" thousands of its US customers avoid tax by opening Swiss accounts on their behalf, a report has claimed.
The bank helped clients create offshore entities and complete transactions in a way designed to avoid arousing suspicion, the report from the Senate's Permanent Subcommittee on Investigations alleges.
The Swiss accounts contained assets totalling $12bn (£7.2bn) at their peak, it is claimed.
Credit Suisse's private banking and wealth management division has already set aside 175m Swiss francs (£118m) to fight a US investigation into hidden offshore accounts in Switzerland. It declined to comment on the latest report.
Prosecutors in the US are chasing 14 Swiss banks for allegedly helping wealthy Americans dodge US taxes.
The subcommittee's report claims: "From at least 2001 to 2008, Credit Suisse employed banking practices that facilitated tax evasion by US customers."
It said the practices included "opening undeclared Swiss accounts" or accounts to "mask their US ownership", as well as sending Swiss bankers to the US to recruit new customers and "service existing Swiss accounts without creating paper trails".
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