French authorities are formally investigating UBS for allegedly helping wealthy clients open undeclared bank accounts in Switzerland, reports the BBC.
The Swiss bank is suspected of "complicity in illegal sales practices", an official at the Paris prosecutor's office told the BBC.
It also allegedly set up a shadow accounting system that masked transfers between French and Swiss bank accounts.
UBS said it was cooperating with authorities.
Under French law being placed under official investigation means there is "serious or consistent" evidence to implicate a suspect in a crime. But it does not necessarily lead to a trial, the official said.
The latest move follows action taken against the bank's French unit last week which was also formally placed under investigation.
Read more of this report from the BBC.
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