Amini, a 22-year-old Iranian Kurd, died a few days after her arrest by religious police for allegedly violating the strict dress code for women in force since shortly after the 1979 Islamic Revolution. Her family says she died from a blow to the head but this is disputed by Iranian authorities.
Anger over her death rapidly expanded into weeks of taboo-breaking protests which saw women tearing off their mandatory headscarves in an open challenge to the Islamic republic's system of government under supreme leader Ayatollah Ali Khamenei.
Reports from outside Iran said the father of Mahsa Amini was briefly arrested on Saturday morning before being later released, as official pressure grows on the family not to held a memorial ceremony for her.
Amjad Amini was detained while exiting the family home in the western town of Saqez and then released after being warned not to hold the memorial service, the Kurdistan Human Rights Network and 1500tasvir monitor said.
Official news agency IRNA described the reports of the arrest as "false", saying they were aimed at "inciting the population to protest".
Amjad Amini was already summoned by intelligence officials last week after his announcement he planned to hold a memorial ceremony. One of Amini's uncles, Safa Aeli, was detained in Saqez on September 5 and remains in custody.
There was no sign of the ceremony taking place at her grave at the Aichi cemetery in Saqez, with some reports suggesting security forces had blocked access to the site.
'Chokehold on dissent' The protests lost momentum after several months in the face of a crackdown that saw security forces kill 551 protesters, according to Norway-based Iran Human Rights, and arrest more than 22,000, according to Amnesty International.
Iranian authorities say dozens of security personnel were also killed in what they describe as "riots" incited by foreign governments and hostile media.
Seven men have been executed after being convicted in protest-related cases.
Campaigners say the authorities have renewed their crackdown in the runup to the anniversary, putting pressure on relatives of those killed in the protests in a bid to stop them speaking out.
New York-based Human Rights Watch said family members of at least 36 people killed or executed in the crackdown had been interrogated, arrested, prosecuted or sentenced to prison over the past month.
"Iranian authorities are trying to impose a chokehold on dissent to prevent public commemoration of Mahsa Jina Amini's death in custody, which has become the symbol of the government's systematic oppression of women, injustice and impunity," said HRW's senior Iran researcher, Tara Sepehri Far.
Kurdish-focused group Hengaw said people in western Iran were expressing discontent through a general strike, with shops shut down in a dozen towns and cities including Saqez.
Hengaw said "repressive forces" were deployed around the Amini family residence in Saqez, adding that the government had in the days leading up to the anniversary sent in additional security forces to the region.
Persian-language channels based outside Iran, including Iran International, broadcast footage of residents shouting "Death to the dictator" and the main protest slogan of "Woman, Life, Freedom" from apartment blocks in Tehran and its satellite city of Karaj overnight.
'Doubling down' While some women are still seen walking in public without headscarves, particularly in wealthy, traditionally liberal areas of north Tehran, the conservative-dominated parliament is currently considering a draft law that would impose far stiffer penalties for non-compliance.
"The Islamic republic is doubling down on repression and reprisals against its citizens and seeking to introduce new and more draconian laws that severely restrict further the rights of women and girls," said Sara Hossain, the chair of the UN fact-finding mission set up to investigate the crackdown.
Under the slogan "Say her name!", Iranian emigrés are expected to hold commemorative rallies, with large demonstrations expected in Paris and Toronto.
Amnesty International accused Iran's authorities of committing a "litany of crimes under international law to eradicate any challenge to their iron grip on power" and lamented that not a single official had been even investigated over Amini's death or the crackdown.
On the eve of the anniversary, Iran's arch-foe the United States and its Western allies including Britain and the European Union imposed new sanctions on the Islamic republic over its protest crackdown.
Announcing the measures, US President Joe Biden led international calls in solidarity with Iranians on the anniversary of Amini's death.
"Iranians alone will determine the fate of their country, but the United States remains committed to standing with them," he said.
Iran's foreign ministry spokesman Nasser Kanani slammed the Western countries' "illegal and undiplomatic actions" in a statement late Friday.
