Protests have swept Iran since the death in custody of Mahsa Amini, a 22-year-old Iranian Kurd who died in mid-September after her arrest for an alleged breach of the country's strict dress code for women.
Mohsen Shekari was hanged Thursday after being convicted for blocking a Tehran street and wounding a paramilitary on September 25, after a legal process that rights groups denounced as a show trial.
The judiciary said the 23-year-old was arrested after striking a member of the Basij -- a paramilitary force linked to the powerful Islamic Revolutionary Guard Corps -- with a machete, a wound that required 13 stitches.
He was convicted last month of "moharebeh", or "enmity against God" -- a capital offense in the Islamic republic.
The announcement sparked an international outcry and warnings from human rights groups that more hangings were imminent.
Amnesty International said it was "horrified" by the execution, which followed Shekari's condemnation in a "grossly unfair sham trial".
"His execution exposes the inhumanity of Iran's so-called justice system" where many others face "the same fate", it added.
Mahmood Amiry-Moghaddam, director of the Oslo-based group Iran Human Rights (IHR), urged a strong international reaction to deter the Islamic republic from carrying out more executions.
"Mohsen Shekari was executed after a hasty and unfair trial without a lawyer," he said.
Calls for more protests
Shekari's body was buried 24 hours after his execution in the presence of a few family members and security forces in Tehran's Behesht-e Zahra cemetery, the 1500tasvir social media monitor reported.
His execution has triggered fresh protests and calls for more demonstrations.
Overnight, protesters took to the street where Shekari was arrested, shouting, "They took away our Mohsen and brought back his body," in a video shared by 1500tasvir.
Elsewhere, chants of "Death to the dictator" and "Death to Sepah" were heard at a demonstration in Tehran's Chitgar district, in reference to supreme leader Ayatollah Ali Khamenei and Iran's Revolutionary Guards.
Hamed Esmaeilion, an Iranian-Canadian activist who has organised mass protests in Berlin, Paris and other cities, said more demonstrations would be held at the weekend.
"Regardless of belief and ideology, let's join these gatherings in protest against the brutal execution of #MohsenShekari," he tweeted.
'Contempt for human life'
1500tasvir said Shekari's execution happened with such haste that his family had still been waiting to hear the outcome of his appeal.
It posted harrowing footage of what it said was the moment his family learnt the news outside their home in Tehran, with a woman doubled up in pain and grief, repeatedly screaming the name "Mohsen!"
Western governments also expressed anger.
Washington called Shekari's execution "a grim escalation" and vowed to hold the Iranian regime to account for violence "against its own people."
Italian Prime Minister Giorgia Meloni expressed indignation at "this unacceptable repression" which, she said, would not quash the protesters' demands.
German Foreign Minister Annalena Baerbock had a similar message.
"The threat of execution will not suffocate the will for freedom," she tweeted, criticising a "perfidious summary trial".
"The Iranian regime's contempt for human life is boundless," Baerbock added.
Germany also summoned the Iranian ambassador, a diplomatic source said, without providing further details.
UK Foreign Secretary James Cleverly expressed outrage and urged the world not to ignore "the abhorrent violence committed by the Iranian regime against its own people."
The office of the UN High Commissioner for Human Rights said it deplored Shekari's hanging.
According to rights group Amnesty International, Iran executes more people annually than any nation other than China.
IHR, which says the security forces have killed at least 458 people in the protest crackdown, this week warned Iran had already executed more than 500 people in 2022, a sharp jump on last year's figure.
At least a dozen other people are currently at risk of execution after being sentenced to hang in connection with the protests, human rights groups warned.