At least 92 people have been killed during protests in Iran over the death of Mahsa Amini following her arrest by the morality police, the Iran Human Rights group said on Sunday.

Kurdish Iranian Amini, 22, was pronounced dead on September 16 after she was detained for allegedly breaching rules requiring women to wear hijab headscarves and modest clothes.

It has sparked Iran's biggest wave of popular unrest in almost three years. 

Solidarity rallies with Iranian women - who have defiantly burnt the hijabs they have had to wear since the 1979 Islamic revolution - have been held worldwide, with demonstrations in more than 150 cities on Saturday.

Clashes between Iranian protesters and security forces have rocked cities nationwide for 16 nights in a row after they first flared in western regions home to Iran's Kurdish minority, from where Amini hailed.

Iran's leading ultraconservative daily Kayhan, whose director is appointed by supreme leader Ayatollah Ali Khamenei, said its Tehran headquarters was attacked by "rioters" and "thugs" on Saturday, some hurling Molotov cocktails.

IHR director Mahmood Amiry-Moghaddam urged the international community to take urgent steps against the Islamic republic to stop the killing of Iranian protesters, saying it amounted to "crimes against humanity".

At least 92 protesters in the Mahsa Amini rallies have been killed so far, said IHR, which has been working to assess the death toll despite internet outages and blocks on WhatsApp, Instagram and other online services. 

London-based Amnesty International said earlier it had confirmed 53 deaths, after Iran's semi-official Fars news agency said last week that "around 60" people had died.

As Tehran was also battling unrest in the country's southeast, it said five Revolutionary Guards members were killed in clashes on Friday in Zahedan, the capital of Sistan-Baluchestan province.

The poverty-stricken region has often seen clashes with Baluchi minority rebels, Sunni Muslim extremist groups and drug smuggling gangs.

But a Sunni Muslim preacher, Molavi Abdol Hamid, said the community was "inflamed" after the alleged rape of a teenage girl by a police officer in the province, in a post on the cleric's website on Wednesday.

IHR accused the security forces of the mainly Shi'ite country of "bloodily repressing" the Zahedan protest that erupted after Friday prayers over accusations a police chief in the province's port city of Chabahar had raped a 15-year-old girl from the Sunni Baluch minority.

Iran has accused outside forces of stoking the nationwide protests, especially its arch enemy the United States and Washington's Western allies.

Iran's intelligence ministry said on Friday that nine foreign nationals - including from France, Germany, Italy, the Netherlands and Poland - were arrested "at or behind the scene of riots", along with 256 members of outlawed opposition groups.

The unrest comes as Iran seeks to revive its 2015 nuclear deal with the United States and other major powers to end sanctions that have throttled its oil-rich economy and seen South Korea and Japan freeze billions of dollars in Iranian funds.

The landmark Vienna deal - which had promised sanctions relief in return for strict nuclear controls - has been in tatters since then US president Donald Trump withdrew from it in 2018 and Iran later backed away from its own commitments.

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In a rare concession, Iran has allowed a detained Iranian-American, Baquer Namazi, 85, to leave the country and released his son Siamak Namazi, 50 from detention, the United Nations confirmed.

Baquer Namazi is a former UNICEF official who was detained in February 2016 when he went to Iran to press for the release of Siamak, who had been arrested in October of the previous year.

Both were convicted of espionage in October 2016 and sentenced to 10 years in prison.

Iranian state media said on Sunday that, following the prisoner release, Iran was now awaiting the unfreezing of about $7 billion in funds abroad.

"With the finalisation of negotiations between Iran and the United States to release the prisoners of both countries, $7 billion of Iran's blocked resources will be released," said state news agency IRNA.