WASHINGTON (Reuters) - U.S. federal prosecutors have launched a new probe into whether Swiss bank UBS AG helped Americans evade taxes through investments banned in the United States, the Wall Street Journal reported, citing people familiar with the investigation.

UBS, which paid US$780 million in 2009 to settle a separate Justice Department tax-evasion probe, is now under investigation for allegedly helping wealthy clients hide assets through so-called bearer securities, the paper said.

Bearer securities, which can be transferred without needing to register ownership, is largely restricted in the United States because they can be used for evading taxes and money laundering. Bearer bonds were often used by U.S. companies to issue debt in foreign countries.

Prosecutors in the U.S. attorney's office in Brooklyn are looking into evidence gathered by the Federal Bureau of Investigation to find out whether the bank's employees helped clients to evade taxes or engage in securities fraud, the Journal reported.

Prosecutors are also investigating whether any executive was involved in criminally covering up any fraudulent conduct.

Authorities recently subpoenaed UBS regarding the investigation, and prosecutors and FBI agents visited London to interview potential witnesses, the report said.

UBS has hired a partner at Wachtell, Lipton, Rosen & Katz, to conduct an internal investigation, the Journal reported.

A UBS spokeswoman declined to comment on the report.