Iranian state-run television showed two detained Iranian-Americans on Monday and promised more images in coming days.
The footage was undated, but the television advertised at the bottom of the screen that it would follow with a full broadcast on Wednesday evening at 21:45 local time (GMT 18:45).
The television images followed Iran's announcement earlier in July that fresh evidence had pushed its judiciary to launch new investigations into the cases of both Haleh Esfandiari and Kian Tajbakhsh, held on charges of endangering national security.
Esfandiari, director of the Middle East program at the Woodrow Wilson International Center for Scholars, was jailed in early May.
The Wilson Center had said she was being held in solitary confinement in Tehran's notorious Evin prison without access to her family, lawyers or international rights organizations.
Tajbakhsh, 45, an urban planning consultant with George Soros' Open Society Institute is also being held on security charges.
Two other Iranian-Americans, Parnaz Azima, a journalist who works for the U.S.-funded Radio Farda, and Ali Shakeri, a founding board member of the University of California, Irvine, Center for Citizen Peacebuilding, are facing similar charges.
Family members, colleagues and employers of the four have denied the allegations.
Shakeri is in custody, while Azima is free but barred from the leaving the country.
The Iranian Intelligence Ministry has accused Esfandiari and her organization of trying to set up networks of Iranians with the ultimate goal of creating a "soft revolution" in Iran to topple the hardline Islamic regime, along the lines of the revolutions that ended communist rule in eastern Europe.
International human rights groups, including the New York-based Human Rights Watch, have expressed deep concern for the health of the detained Americans - especially Esfandiari, who is 67.
Esfandiari has been trapped in Iran since visiting her 93-year-old mother in December, when three masked men with knives stole her luggage and passport as she headed to the airport to leave, according to the Wilson Center.