A senior Iranian justice official has offered his resignation in protest against the death sentence passed on a liberal academic, Hashem Aghajari, for blasphemy.

The official, Hussain Mir-Mohammad Sadeghi, who is the spokesman for the judiciary, said the ruling has damaged Iran.

Let us in - we will show you what we do with people who want a referendum Conservative demonstrators

News of the resignation became public as an estimated 500 students were forced to barricade themselves into a campus building when a lecture was interrupted by members of an ultra-conservative militia.

Separately, a leading reformer - Mohammad Reza Khatami, the brother of Iranian President Mohammad Khatami - warned conservatives that if they did not listen to students' demands, they would face the same fate as the late Shah of Iran, who was deposed.

Referendum demand

Students have been holding almost daily demonstrations for a month, following the death sentence imposed on Mr Aghajari in November.

They have been demanding a referendum on the future of the country.

Iran's Supreme Leader has intervened

They were the largest pro-reform demonstrations in Iran for more than three years and quickly brought a ban on such protests.

On Tuesday, members of the Basij militia stormed a speech by Ebrahim Yazdi, the head of the Iran Freedom Movement, at Tehran's Alameh university.

Windows were broken in the incident, but there were no reports of major violence. The barricaded students reportedly escaped through a back door.

Rare break in ranks

Mr Mir-Mohammad Sadeghi's resignation signalled rare public disagreement among senior conservative officials.

Although his resignation was handed in 10 days ago, the head of the judiciary has yet to accept it.

President Khatami criticised the death sentence

In June, the history lecturer enraged conservatives by saying that Muslims should not follow the line laid down by Islamic clerics "like monkeys".

In an interview with Iran's official news agency, Mr Mir-Mohammad Sadeghi criticised what he called the growing politicisation of the Iranian judiciary.

He said the death sentence against Mr Aghajari had catastrophic consequences for the judiciary and the country as a whole.

Such an open broadside coming from within the conservative faction itself may mean that hard-line leaders may find it difficult to preserve their unity in the face of serious crisis, BBC Iran analyst Sadeq Saba says.

Mr Aghajari's sentence is now under judicial review following an order from supreme leader Ayatollah Ali Khamenei.