As the US tax authorities continue their crackdown on people using offshore tax shelters, a lawyer and an accountant have been indicted for conspiring to defraud the Internal Revenue Service and helping clients file false returns, media reports said.

The men are Steven Allen, an attorney who operated a legal practice in Mesa, Arizona, and Allen Goodmansen, a certified public accountant who operated an accounting practice in Mesa.

Mr Goodmansen was also charged with knowingly filing a false personal income tax return for tax year 2002.

According to the indictment, from at least 1997 through 2004, the men and others participated in a scheme to help clients unlawfully evade the payment of income taxes. 

US public authorities, with strong backing from president Barack Obama and lawmakers, are mounting an increasingly loud campaign against offshore financial jurisdictions in a bid to stem an outflow of tax revenues.