Former Iranian president Mohammad Khatami has voiced support for the protest movement sparked by Mahsa Amini's death, describing as "beautiful" its main slogan -- "Woman, life, freedom".

Protests have swept Iran for nearly three months since Amini died after her arrest for an alleged breach of the country's hijab dress code for women based on Islamic sharia law.

The authorities, who have struggled to contain the protests, describe them as "riots" fomented by Iran's arch foe the United States and its allies including Britain and Israel.

Khatami, a reformist who served as Iran's president from 1997 to 2005 but has been effectively silenced by the establishment for years, has come out in support of the movement.

The 79-year-old described the slogan "Woman, life, freedom" -- the main chant heard at the protests -- as "a beautiful message that shows movement towards a better future".

"Freedom and security must not be placed against each other," he said in a statement quoted by ISNA news agency Tuesday, on the eve of Students' Day.

"Freedom must not be trampled on in order to maintain security" and "security should not be ignored in the name of freedom," he said.

Khatami also spoke out against the arrest of students who have been at the forefront of the protests that erupted across Iran since Amini's death in custody on September 16.

The imposition of restrictions "cannot ultimately ensure the stable security of universities and society", he said.

In his statement, Khatami also called on officials to "extend students a helping hand" and to recognise the "wrong aspects of governance" with their help before it is too late.

Khatami was barred from appearing in the media after mass protests triggered by the disputed 2009 re-election of former president Mahmoud Ahmadinejad.

Iran's top security body, the Supreme National Security Council, said on Saturday that more than 200 people have been killed in the unrest.

An Iranian general said last week that more than 300 people have been killed in the unrest, including dozens of security personnel.

Norway-based non-governmental organisation Iran Human Rights said on November 29 that at least 448 people had been "killed by security forces in the ongoing nationwide protests".

Thousands have been arrested, including prominent Iranian actors and footballers.