ONE OF America's foremost foreign affairs reporters, Seymour Hersh, has claimed America is running a covert operation into Iran, funded by $US400 million ($A414 million) siphoned from other programs, with authorisation from Democratic congressional leaders.

According to Hersh, a journalist with the New Yorker magazine, Congress agreed to a request from President George Bush late last year to pay for a significant escalation of covert operations against Iran.

He said these included activities by the the Central Intelligence Agency and the Joint Special Operations Command, and involve support of the minority Ahwazi Arab and Baluchi groups and other dissident organisations.

They also included gathering intelligence about Iran's suspected nuclear-weapons program.

Hersh said covert operations were not new but had been stepped up dramatically in recent months, causing disquiet in Congress.