Iranian TV has shown the first pictures of two Iranian American academics - Haleh Esfandiari and Kian Tajbakhsh - who have been held in Iran since May.

The footage was a trailer promoting a programme to be aired later this week.

Only snatches of their voices are heard but the BBC's Tehran correspondent says they appear to be confessing to trying to topple the Iranian government.

Ms Esfandiari, Mr Tajbakhsh and another detained Iranian American, journalist Parnaz Azima, are accused of spying.

They could face the death penalty if found guilty.

In the footage, Ms Esfandiari and Mr Tajbakhsh appear to be saying they were working towards a peaceful revolution in Iran - like those that toppled the government in the former Soviet republic of Georgia.

The state TV also showed glimpses of the recent revolutions in Georgia and Ukraine.

Ms Esfandiari was dressed in a black Islamic veil and coat. Both she and Mr Tajbakhsh appeared in good health.

Tehran has accused Washington of using intellectuals and others to try to undermine Iran's Islamic authorities. The US denies the accusation.