WASHINGTON, USA - A US tax probe into bank accounts held by wealthy Americans with Swiss banking giant UBS heated up on Tuesday, as a judge authorised investigators to seek financial information from the bank.

The Justice Department said a US federal judge in Miami, Florida, had issued an order earlier Tuesday authorising the Internal Revenue Service (IRS) to request information from Zurich-based UBS about certain US taxpayers.

Investigators believe wealthy Americans may be using Swiss bank accounts to evade US income taxes on billions of dollars of assets.

Banks often advise wealthy clients on how to legally minimise their tax bills, but it is illegal in the United States to actively evade paying income tax on earnings.

The Florida court order by US District Court judge Joan Lenard - which was released by the Justice Department - authorises the IRS to serve a summons for information on UBS.

The summons directs the Swiss bank to produce records identifying US taxpayers who hold accounts with UBS in Switzerland.

Former UBS banker Bradley Birkenfield has told the court that UBS bankers helped affluent American clients improperly conceal assets offshore by creating 'sham entities.'

Birkenfield has already pleaded guilty to conspiring to help US clients evade millions of dollars in taxes by hiding assets in Switzerland and the secretive European principality Liechtenstein.

The UBS-focused probe comes after US tax authorities opened an investigation of over 100 Americans in late February related to bank accounts held Liechtenstein.

The Justice Department said Tuesday that UBS employees had filed false reports with the IRS claiming that the 'sham entities' were the owners of certain accounts.

Birkenfield has told the court in a statement that UBS managed US$20 billion of assets in 'undeclared' bank accounts on the behalf of US taxpayers.

Media reports have suggested that the US Federal Bureau of Investigation is also supporting the Justice Department's inquiries into possible tax evasion by wealthy Americans.