An Iranian opposition group is reported to have claimed responsibility for mortar attacks on the offices of President Mohammad Khatami, which killed one man.

The Iraq-based Mujahideen Khalq said it timed the assault on government buildings in southern Tehran to disrupt the 21st anniversary of Iran's Islamic Revolution next week.

Iranian state TV also blamed the group for the attack.

It said a 34-year-old man who worked in a print shop near the presidential office had been killed.

At least five people other people were said to be injured, it added.

Mr Khatami was reportedly in the building at the time of the attack, but is said to have escaped injury.

Witnesses said other mortar rounds, apparently aimed at nearby government installations, blew out windows and damaged offices.

Among the offices hit was the central administrative office for Iran's Friday prayers apparatus, located next door to the presidency.

Police closed off the roads leading to the area and turned away reporters.

Iran is preparing for key parliamentary elections on 18 February and the authorities have been braced for possible unrest.

Rising tension

The attack came as Iran celebrates the anniversary of the Islamic revolution, which overthrew the Shah 21 years ago - an occasion when security forces are always on the alert for possible attacks by the Mujahideen.

But it also came as the country prepares for hotly-contested general elections, in just under two weeks' time, in which supporters of Mr Khatami, are hoping to win power from the currently-predominant conservatives.

Political tension has been rising with the approach of polling.

In the holy city of Qom, south-east of Tehran, thousands of hardline seminary teachers and students have, for the past three days, been staging a protest sit-in at a mosque, demanding the dismissal of one of President Khatami's closest associates, the culture minister, Ataollah Mohajarani.

The protest was triggered by the publication of a cartoon in a reformist newspaper, portraying a senior cleric as a crocodile.

But the sit-in has now been called off after the country's supreme leader, Ayatollah Ali Khamenei, thanked the protestors and asked them to stand down because of the sensitivity of the current situation.

The leader said he approved of their demand for a change in the country's cultural situation.