Iranian state television, controlled by conservatives in the Islamic regime, has taken the rare step of giving airtime to a high-ranking member of a silenced reformist opposition leader's party.

Javad Haghshenas was a founding member of Etemad Melli (National Confidence), the party led by Mehdi Karroubi, a former parliament speaker held under house arrest since February 2011 for disputing the result of a presidential election two years earlier.

Karroubi, a candidate, and Hossein Moussavi, a fellow reformist who declared he had won the ballot and who is also under house arrest, are denounced by hardliners as seditionists who tried to fell the regime.

The contested poll result gave birth to the country's so-called Green Movement, but incumbent Mahmoud Ahmadinejad, a hardline conservative, was officially declared the winner.

Street protests that followed were put down by the authorities, with dozens of civilians killed in the biggest political crisis in the country since the 1979 revolution that overthrew the Shah.

On Monday night Haghshenas was a guest in a head-to-head debate with Hamid Reza Taraghi, a conservative politician, about President Hassan Rouhani's first two years in power.

The programme, which was repeated on Tuesday morning, normally features supporters and opponents of the government but the latest edition was more notable for Haghshenas inclusion.

The one-hour programme focused on a spate of concerts which, despite being approved by the culture ministry, have been cancelled at the last minute by other authorities with little explanation.

Karroubi and Moussavi, a former prime minister, face an uncertain future. Some want them to face trial, and their fiercest opponents say they should be executed.

Their images are banned in Iranian media. They were placed under house arrest at the same time after calling for fresh demonstrations to try to revive the Green Movement.

Although the reformist camp fell into the wilderness afterwards, and two parties were outlawed, Karroubi's National Confidence was not banned.

Two new reformist parties -- Nedaye Iranian (Voice of Iranians) and Ettehad Mellat Iran (Iranian National Unity) -- have also been formed ahead of legislative polls next February.

Rival parties are already positioning themselves for those elections. On Tuesday it was announced that 10 former ministers and officials from Ahmadinejad's government have formed a new party.

Yekta (Unique -- an acronym for the "Companions of the competence and evolution of the Islamic Republic) said it had programmes for all areas of government, but no official links with the former president.

Ahmadinejad has kept a low profile since leaving office, but he made a limited return to the political scene in February by creating a new official website.