The United States says it is "appalled" at the treatment of four US-Iranians detained in Tehran after Iranian television aired footage of two academics ahead of their alleged "confessions".
"We are outraged that the government of the Islamic republic of Iran would parade two of these American citizens on state-run television on July 16," State Department spokesman Sean McCormack said in a statement.
He was speaking after Iran on showed the first footage of two academics, Haleh Esfandiari and Kian Tajbakhsh, whose detention on charges of harming national security has raised tensions with Washington.
The images of the two talking to the camera were a promotional trailer for a longer program to be shown tomorrow as Iranian television said it would broadcast confessions from the pair.
Snippets showed by Iranian television showed them apparently linking themselves to alleged US efforts to weaken Iran's Islamic authorities.
But McCormack said the two were "apparently reading statements made under duress".
"These two individuals have laboured for years to build bridges of understanding between our two countries; their efforts should be recognised as a benefit to both our nations," he added in his statement.
"We call upon Supreme Leader Ali Hosseini Khamenei to treat these people with the respect they deserve, to put an end to any further broadcasts, and to release all Americans currently being held on groundless charges."
Both academics have been linked to an alleged US drive to topple Iran's Islamic authorities through a "Velvet Revolution" under theguise of promoting democracy.
It was not clear where or when the footage was recorded. Both academics are believed to be held in Tehran's Evin prison.
Esfandiari, 67, heads the Middle East program at the Washington-based Woodrow Wilson International Centre for Scholars.
She was arrested after returning to Iran late last year to visit her ailing 93-year-old mother.
Tajbakhsh is an urban planning expert who had ties with the Open Society Institute of US billionaire George Soros, accused by Iran of seeking a peaceful revolution similar to the toppling of communism in Eastern Europe.
Two other US-Iranians face similar charges, but were not referred to in the footage.
California-based businessman Ali Shakeri has also been detained. Parnaz Azima, a journalist for Radio Free Europe's Persian arm, is technically at liberty but has had her passport confiscated and cannot leave the country.
"The United States is appalled at the mistreatment of Americans," McCormack said, mentioning the four by name and adding they were "prevented by authorities from departing Iran".
He also renewed US calls for Tehran to provide information about a missing former FBI agent Robert Levinson who vanished while on a private visit to the southern Kish Island in March.
Despite Washington's demands, Iran has repeatedly said that it has no knowledge of Levinson's whereabouts.