Women may be forced to run on an indoor track during what has been described as Tehran’s “first international marathon” on Friday.

‘TehRUN’, in Iran’s capital, is expecting 600 Iranian participants, including 156 women, and 160 foreign runners, among them 50 women, to take part in what its website describes as an opportunity for “building bridges, breaking barriers.”

Female participants were dismayed to be told in an email from the organisation three weeks ago that they would no longer be allowed to take part in the race.

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Non-profit ‘Free to Run’, which encourages women and girls mainly from conflict areas to participate in sport and experience the outdoors, said in a Facebook post on Sunday that the authorities had been listening to the concerns of female runners and it appeared that women would be allowed to compete after all.

However, it emerged on Wednesday - just two days before the race - that women participants would not be allowed to take part in the official route, and instead run the 26 miles (42 kilometres) inside a stadium.

“Personally I do not agree with that and we are trying to find other ways to make step(s forward) for female running in Iran,” Dutch race organiser Sebastiaan Straten said.

Since the 1979 revolution Iranian women have had to follow a strict dress code in public. The race website asks female runners to “In general dress modestly to respect local customs and religion,” by wearing long-sleeved t-shirts that cover the hips, and headscarves or bandanas over their hair.

Anyone cheering on women participants at the stadium on Friday will also be female, since the Iranian religious authorities forbid men and women to watch sports in which the opposite gender is competing.

Majid Keyhani, the head of Iran's track and field federation, said that although no professional runners were taking part this year he hoped they would enter the ‘Persian Run’ in future.

Friday’s event follows the race’s first incarnation in 2016 in Marvdasht. No women were allowed to officially take part last year, but two women - Masoumeh Torabi and Elham Manoocheri - nonetheless ran separately from the men in protest, and are recognised as participants on the race’s website.