The American Iranian Council (AIC), a research and policy think tank devoted to improving ties between the two arch enemies, was given a license to establish a presence in Tehran by the US Treasury Department's Office of Foreign Assets Control (OFAC), officials said.
"We understand that a license has been granted to the American-Iranian Council but would refer you to the Office of Foreign Asset Control at the Treasury Department for any information regarding OFAC licenses," the office of State Department spokesman Sean McCormack said.
The OFAC enforces US sanctions against countries such as Iran, Sudan and Cuba.
Treasury Department spokesman Robert Saliterman told AFP that the department "does not confirm or deny the issuance of licenses."
But, he added that "licenses for NGOs are based on foreign policy guidance."
McCormack's office explained that US policy towards Iran "has not changed" with the approval given to AIC.
"We encourage efforts to increase people-to-people contacts between the people of Iran and the people of the United States in order to expand mutual understanding, as long as parties involved work in accordance with US laws and regulations," the statement said.
The AIC will be the only US-based peace and conflict resolution, non-governmental organization operating in Iran, said its executive director, Brent Lollis.
"We look forward to helping governmental officials, NGO officials, and especially common citizens in working with us to promote respectful, rational and direct dialog between the United States and Iran," he said in a report on the group's website.
"This AIC office is a first step on the path to the institutionalization of a normalized relationship," he said.
US and Iran have no diplomatic relations, broken off in 1980 after Islamist students took US diplomats hostage at the embassy in Tehran.
Over the past years, Washington has taken a tougher line toward the Islamic republic, accusing it of backing armed groups in Iraq, thwarting any Middle East settlement with its support for the Palestinian Islamist Hamas movement and Lebanon's Shiite militia Hezbollah, and using its nuclear program as a cover to acquire nuclear arms.