Tehran residents are unused to a US NGO presence in their city
Washington has given rare approval for a research body to open an office in Iran, although it stressed United States policy had not changed.
The American Iranian Council was given a licence to establish a presence in Tehran by the US Treasury Department.
The Treasury's Office of Foreign Asset Control enforces US sanction on Iran.
The AIC is a policy think tank devoted to improving relations between the US and Iran, which have been mutually hostile since Iran's 1979 revolution.
A spokesman for the US state department, which guides the policy for issuing non-governmental organisation (NGO) licences to places under US sanctions, like Iran, Sudan and Cuba, said the move did not signal any change in policy.
US and Iran have had no diplomatic relations since the US hostages crisis in 1980 when Islamic revolutionary students took over the US embassy in Tehran.
The executive director of the think tank, which based at Princeton, New Jersey said the licence would allow it to become only US-based peace and conflict resolution NGO operating in Iran.
"We look forward to helping governmental officials, NGO officials, and especially common citizens in working with us to promote respectful, rational and direct dialogue between the US and Iran," Brent Lollis announced on the group's website.
A US official quoted by the Reuters news agency said the establishment of an AIC office in Tehran would encourage cultural exchange and "mutual understanding" between peoples while "trying to isolate the Iranian regime".
Iran has in the past year accused the US of using academic exchanges and think-tanks to undermine the Islamic republic and it has charged three visiting US-Iranian scholars with espionage.
It is not known if the AIC has been given permission to set up its office in Tehran.