The wife of the strongest challenger to Iranian President Mahmoud Ahmadinejad has threatened to sue him for defamation.

Rallies for Mir Hussein Moussavi, a reformist who is the leading contender to defeat Ahmadinejad in the election set for Friday, have drawn tens of thousands of people in recent days. A new unofficial poll suggests his support has markedly increased, with 54 per cent of respondents saying they would vote for him compared with 39 per cent for Ahmadinejad.

Many see this as a result of last Wednesday’s nationally televised debate, in which the President opened with a furious attack on Moussavi, and his wife. Ahmadinejad held up a document with a small picture of Moussavi’s wife, Zahra Rahnavard, and asked him: “Do you know this woman?” Ahmadinejad then accused Rahnavard — a respected professor of political science — of entering a graduate programme without taking the entrance exam and other, lesser violations of university policy.

The attack on Rahnavard struck a nerve. She has taken an unusually public role in her husband’s campaign, and many liberal Iranians feared that Ahmadinejad’s attack was code for a broader effort to deny women a public role.

On Sunday, Rahnavard said at news conference: “The way the President insulted me was an insult to everyone... Those who made up this case against me wanted to say it is a crime for women to study...”