The US and Swiss governments Sunday called for a delay to the start of a court showdown seeking to force Swiss financial giant UBS to reveal thousands of offshore accounts held by US clients.

"Petitioner USA and respondent UBS AG jointly move with the support of... the government of Switzerland for a stay in order to allow the two governments to continue their discussions seeking a resolution of the matter," according to a US Department of Justice document published Sunday.

A court showdown had been set to begin Monday in a Miami court pitting UBS against American tax authorities in a key test for Switzerland's long tradition of bank secrecy.

US authorities are asking a federal court to order UBS to reveal the names of American offshore account holders, saying the Swiss bank "systematically and deliberately" violated US laws.

The case stems from a lawsuit filed earlier this year and affects as many as 52,000 US taxpayers suspected of holding UBS offshore accounts to avoid paying US taxes.