The US government has stepped up the pressure on Switzerland’s UBS to disclose the identities of 52,000 US clients accused of evading taxes, according to court papers, media reports said.

“UBS must disclose the identity of every US taxpayer with an undisclosed UBS account” so they can “get right with their government,” the Justice Department filing said. “The United States has a strong national interest in making sure that all US taxpayers comply with the tax laws,” according to papers filed in a Miami court by the US Justice Department.

The bank’s clash with US legal authorities comes at a time when large economic powers such as the US and the UK, both with massive budget deficits, have been putting pressure on offshore financial centres to divulge more information about people using offshore accounts. Defenders of offshore centres say the pressure is in some cases hypocritical, since both the US and UK operate tax havens in places such as the Channel Islands or the US state of Delaware.

In February, the US government sued UBS demanding details about its US clients. The Swiss firm has already ceased providing offshore banking accounts for US citizens and has agreed to pay a $780 million fine after admitting helping US citizens evade taxes.

However, UBS has resisted handing over the names of the estimated 52,000 US clients it has acted for, and the Swiss government has insisted that the Alpine state’s historic bank secrecy laws must not be compromised. A fundamental change to this secrecy law, which dates back centuries, would require domestic legislation in Switzerland.

In court filings and a diplomatic note, the Swiss government has said the lawsuit would “seriously jeopardize” efforts to revise a 1996 tax treaty, media reports said.

Under that treaty, Switzerland can turn over account data only on a reasonable suspicion of “tax fraud or the like,” according to a UBS court filing.

A UBS spokesperson was quoted by Reuters as saying that the bank is "open to an appropriate solution" short of going to court, but said no settlement has been completed.

"UBS has sought to comply with the summons without violating Swiss law," the spokesperson said. "It has provided to the IRS as much information as it can from those records located in the US, where Swiss law does not apply."