However, the jury at a press court in Tehran found Faezah Hashemi guilty of a lesser charge of insulting a senior police chief.

The case was seen by observers as the latest incident in the continuing power struggle between reformers and conservatives.

President Khatami is urging restraint

Ms Hashemi had been accused of publishing lies about police intelligence chief Colonel Mohammad Naqdi by implicating him in an attack on two government ministers.

Her outspoken paper Zan [Woman] quoted witnesses saying they had seen him assaulting former interior minister Abdullah Nouri and culture minister Ataollah Mohajerani.

The two men are both noted supporters of reformist president Mohammad Khatami who have aroused much hostility among religious conservatives.

They were roughed up by hardline thugs during a funeral procession in September.

Ms Hashemi's defence produced a witness who said he had seen Colonel Naqdi taking part in the attack.

But the colonel produced four witnesses who said he was at home at the time.

Ms Hashemi, whose father served twice as Iran's middle-of-the-road president in the 1980s, has increasingly become associated with reformists backing Mr Khatami.

Her paper Zan is one of the country's more outspoken publications, criticising policies and social customs discriminating against women.

Hardliners hitting back

BBC Middle East Correspondent Jim Muir says the struggle between reformists and hardline conservatives is now breaking surface in the country's press, the streets and on the university campuses.

He says the Zan case is seen very much as part of an attempt by the hardline camp to hit back at the progressive supporters of the president.

Many of the millions of Iranians who voted for Mr Khatami last year, in the hope of bringing about change, are becoming impatient at the slow progress being made in the teeth of fierce opposition from the hardliners.

But Mr Khatami has urged critics to exercise restraint and to avoid being drawn into violent confrontations.

Addressing a large crowd of students in Tehran, he said change could only come through political process, tolerance and dialogue.