By Frances Harrison

BBC News, Religous Affairs correspondent



President Ahmadinejad came under criticism from a senior cleric

The remarks have intensified the debate over the return of the Shia saviour, the 12th Imam known as the Mehdi.

Since Mr Ahmadinejad came to power he has repeatedly spoken of the need to plan for the Mehdi's imminent return.

Shia believe he went into hiding more than 1,000 years ago but will return to save the world from injustice.

Scathing criticism

Many Shia clerics do not approve of the cult rapidly growing around the Mehdi.

Iran's former nuclear negotiator, Hassan Rowhani, has complained about what he calls games, superstitions and trickery that make a mockery of the people.

Hassan Rowhani said the 12th Imam himself made it clear that anybody who claimed to have seen him would be a liar.

Mr Rowhani asked how two or three years ago one person could have said the Mehdi would return in a couple of years.

Some Shia believe the 12th Imam will return soon

His government has often discussed plans for the return of the 12th Imam and Mr Ahmadinejad frequently refers to the "Absent Imam" in speeches.

President Ahmadinejad has also spent millions of dollars on a mosque at Jamkaran, south of the capital, where pilgrims post letters with their prayers to the 12th Imam down a well.

Mr Rowhani's attack on those who promote the idea that the saviour will come soon is one of the most scathing by a prominent cleric.

He said when they pray some people already lay another prayer mat for the "Missing Imam". Others set an extra plate on the dinner table for the Imam.

He complained some Iranians were even scheduling meetings on Fridays because that is the day they think the 12th Imam will return.