The National Iranian American Council, in a statement, described them as dual citizens but did not specify their other nationalities
Iran said on Wednesday it would accept no US "interference" after Washington demanded the release of a dual national and his 80-year-old father given 10 year sentences for espionage.
The State Department demanded the immediate release of Siamak and Baqher Namazi, both Iranian-American dual nationals, after their sentences were announced on Tuesday.
But foreign ministry spokesman Bahram Qassemi told Iranian media: "The government and the Iranian people give no importance to the statements and interference of American officials and their efforts to divide the ranks of the Iranian people.
"The American threats only add to the wall of mistrust Iranians have regarding the United States."
Washington expressed concern over the health of the elder Namazi, a former UN Children's Fund employee who also served as the governor of an Iranian province before the Islamic revolution of 1979.
Both were jailed for 10 years for "espionage and collaboration with the American government", Tehran prosecutor Abbas Jafari Dolat-Abadi announced on Tuesday.
Three other Iranians -- Farhad Abd-Saleh, Kamran Ghaderi and Alireza Omidvar -- were also sentenced to 10 years on the same charges.
The National Iranian American Council, in a statement, described them as dual citizens but did not specify their other nationalities.
They were sentenced along with a US resident from Lebanon, Nezar Zaka.
Siamak Namazi, a well-connected business consultant who has supported Iranian reformists and sought to promote ties between Iran and the United States, was arrested as he arrived in Tehran a year ago.
His father was detained in February when he came to Iran to seek his son's release.
Conservatives in Iran have criticised attempts by the moderate government of President Hassan Rouhani to improve ties with the West following a nuclear deal with world powers last year.