DUBAI (Reuters) - An American-Iranian dual national and his wife have been in detention in Iran without charge or access to lawyers since their arrest by elite Revolutionary Guards in July, a New York-based rights group said on Friday.

The International Campaign for Human Rights in Iran (ICHRI) said Karan Vafadari and his wife Afarin Niasari, who run an art gallery in Tehran, were being held in Tehran’s Evin Prison.

The Islamic Republic does not recognise dual nationality, a position that prevents Western embassy officials from visiting such detainees.

“Yet another case of a dual national snatched and held without charge or access to a lawyer represents an alarming continuation of a judicial system run by intelligence agencies with no respect for the law and no accountability,” said Hadi Ghaemi, executive director of the human rights group.

The statement said families of the arrested couple decided not to publicize their cases, hoping it would be resolved.

“Then when the family started receiving anonymous phone threats and demands for money, they decided to go public and write a letter to Iran’s supreme leader,” the statement said.

In the letter to Ayatollah Ali Khamenei, Vafadari’s Washington-based sister Kateh said her sister-in-law was detained at Tehran airport as she was about to board a flight to attend a family wedding abroad, the statement said.

“She was told to call her husband and ask him to come to the airport. When he arrived, he, too, was arrested and both were taken to Evin Prison.”

There was no immediate Iranian comment on the human rights group report.

U.S. State Department spokesman John Kirby said in a news briefing on Friday that U.S. officials were aware of reports that a U.S. citizen and U.S. permanent resident had been detained in Iran, but he declined to comment further.

In August, Tehran Prosecutor Abbas Jafari-Dolatabadi was quoted in Iranian media as saying that two Iranian dual nationals had been arrested the previous week, linking them to a home that had hosted mixed-gender parties for foreign diplomats. Security forces discovered 4,000 liters of alcohol in the home, he said, without naming Vafadari or Niasari.

Only members of religious minorities - Christians, Jews and Zoroastrians - are allowed to brew, distil, ferment and drink liquor discreetly in the privacy of their homes. Trade in liquor is forbidden. The ICHRI said Vafadari is Zoroastrian.

Several people with dual Iranian and foreign nationalities have been arrested in Iran since 2015, when Iran and six major powers reached a nuclear deal at a time of tentative detente after many years of antagonism between Tehran and the West.

An Iranian-American businessman, Siamak Namazi, and his elderly father Baquer Namazi, were sentenced to 10 years in prison in October for collaborating with a foreign government, a sentence their family said was unjust.

In September, the family of Nazanin Zaghari-Ratcliffe, 39, a dual British-Iranian national, was sentenced to five years in jail on charges that were kept secret.

Zaghari-Ratcliffe works for the Thomson Reuters Foundation, a London-based charity that is independent of Thomson Reuters and operates independently of Reuters News. The Foundation and her husband have dismissed Iran’s accusations against her.