Even by the standards of Washington politics it was an unusual spectacle - the veiled leader of a Middle East group banned in the US as a terrorist organisation delivering a speech by live video-link to applauding members of Congress inside the Capitol itself.

But since the organisation is dedicated to the overthrow of Iran's theocracy, the People's Mujahideen Organisation and its political co-leader, Maryam Rajavi, are given leeway in the US as they campaign to have the "terrorist" tag removed and to become eligible for US funding of Iranian opposition groups.