The daily "Vatan-e Emruz" published the interview in its November 3 issue under the headline "America Supports The Saravan Crime." It identifies the interview subject as Abdol Raouf Riggi, who is named as the spokesperson of "Jaish al Adl."
The little-known Sunni group has claimed responsibility for the October 26 killing of 14 Iranian border guards, saying it was in retaliation for the "cruel treatment" of Sunnis in Iran and the "massacre" in Syria it claims is being carried out by Iran.
The daily accused the United States of attempting to create "insecurity" on the Iranian border, with the ultimate goal of spreading insecurity within the country.
"Vatan-e Emruz" further claimed that Radio Farda, RFE/RL's Persian service, has expressed "full support" for the killing of the border guards and interviewed the head of "Jaish al Adl" to pave the way for its future role in Iran.
Radio Farda has categorically denied conducting the interview.
The interviewer, which "Vatan-e Emruz" identified as a Radio Farda broadcaster, referred to the Saravan killing as a "protest action" and asked the purported Jaish al Adl spokesman whether it was "successful."
The interview was reposted by several hard-line websites, including the website of the Fars news agency, which is affiliated with the Islamic Revolutionary Guards Corps (IRGC).
An audio file of the interview was posted on YouTube, incorporating the Radio Farda logo and jingles.
This file has since been removed from the content-sharing site.
It is not clear what role "Vatan-e Emrouz," which is said to be owned by an adviser to former President Mahmud Ahmadinejad, had in producing the interview.
It is also unclear whether a Jaish al Adl spokesman was actually interviewed, or whether audio was lifted from other Farsi-language media.
In the past year, relatives of some of Radio Farda broadcasters and also journalists with the Persian Service of the BBC and VOA have faced pressure from Iranian authorities.