The US treasury department has revealed that one of its officials took part in discussions with Iranian officials in Paris last month.
The talks were multi-lateral, with no one-on-one sessions with Iran
Such meetings are rare as the two countries have no diplomatic relations.
The US says the talks were initiated by an international body set up to monitor the financing of terror groups.
Reports say the session was called at Tehran's request, to respond to claims that it is complicit in money laundering and financing terrorists.
The American official who attended the meeting was named as Daniel Glaser, who is in charge of terrorist financing and financial crimes at the treasury.
The talks were held at the Paris headquarters of the Financial Action Task Force.
In October, a report by the task force said Iran's lack of action to combat terrorist financing was threatening the international financial system.
The US treasury department says the talks were multilateral and that there were no one-on-one talks with Iran.
The Bush administration is currently attempting to step up international pressure on Iran to halt nuclear activities that could lead to the development of nuclear weapons.
The US and Iran have had no diplomatic relations since the 1979 Iranian Revolution and the taking of hostages at the US embassy in Tehran. Formal contact between the two countries is extremely limited.