Shares of UBS plunged Wednesday following a Bloomberg report that the Swiss bank faces a widening probe by the US Department of Justice (DOJ) over suspected compliance failures that allowed Russian clients to evade sanctions.

The Swiss Stock Exchange said it had temporarily stopped trade in the stock, which had fallen as much as 8% before they were suspended. Trading resumed later and shares stood about 3.5% lower by the early afternoon in Zurich.

What began as a probe into several banks earlier this year has turned into a full-scale investigation focusing on Credit Suisse, Bloomberg reported, citing people familiar with the matter.

UBS bought Credit Suisse earlier this year in an emergency rescue deal.

The DOJ has briefed lawyers for UBS (UBS), which absorbed its smaller rival in June, about Credit Suisse's alleged involvement in sanctions violations, according to Bloomberg. Authorities are also looking into possible compliance failures at UBS.

UBS declined to comment. CNN has contacted the DOJ.

— This is a developing story and will be updated.