Iran carried out its first known execution Thursday over the protests that have shaken the regime since September, sparking an international outcry and warnings from rights groups that more hangings are imminent.
Mohsen Shekari, 23, had been convicted and sentenced to death for blocking a street and wounding a paramilitary during the early phase of the protests, after a legal process denounced as a show trial by rights groups.
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.
Demonstrations have swept Iran for nearly three months since Iranian Kurdish woman Mahsa Amini, 22, died in custody after her arrest by the morality police in Tehran for an alleged breach of the country's strict hijab dress code for women.
The protests, described by the authorities as "riots", are posing the biggest challenge to the Islamic republic since it was established following the ouster of the shah in 1979.
"Mohsen Shekari, a rioter who blocked Sattar Khan Street in Tehran on September 25 and wounded one of the security guards with a machete, was executed this morning," the judiciary's Mizan Online website said.
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," the group added.
Mahmood Amiry-Moghaddam, director of Oslo-based group Iran Human Rights (IHR), urged a strong international reaction otherwise "we will face mass execution of protesters".
"Mohsen Shekari was executed after a hasty and unfair trial without a lawyer," he said.
Iran's Fars news agency carried a video report of Shekari talking about the attack while in detention, which IHR described as a "forced confession" with his face "visibly injured".
Western governments echoed the anger of the rights groups.
Washington called Shekari's execution "a grim escalation" and vowed to hold the Iranian regime to account for violence "against its own people."
In Rome, Prime Minister Giorgia Meloni expressed indignation at "this unacceptable repression" which, she said, will 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 after what she called a "perfidious summary trial".
"The Iranian regime's contempt for human life is boundless," Baerbock said.
Germany also summoned the Iranian ambassador, a diplomatic source said later on Thursday, but did not provide any further details about the summoning.
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 "we deplore (the) hanging of" Shekari.
The revolutionary court in Tehran heard Shekari had been arrested after striking the member of the Basij paramilitary force in the shoulder with the blade. The injury required 13 stitches, Mizan Online said.
The Basij is a state-sanctioned volunteer force that is linked to Iran's powerful Islamic Revolutionary Guard Corps.
The court convicted Shekari of "moharebeh" -- or waging "war against God" under Iran's Islamic sharia law -- on November 1, said Mizan.
It added that he appealed but the supreme court upheld the ruling on November 20.
According to Amnesty, Iran executes more people annually than any nation other than China.
IHR this week said Iran had already executed more than 500 people in 2022, a sharp jump on last year's figure.
The 1500tasvir protest monitor said on social media that the execution of Shekari had happened with such haste that his family had still been waiting to hear the outcome of the appeal.
It posted harrowing footage of what it said was the moment his family found out the news outside their home in Tehran, with a woman doubled up in pain and grief, repeatedly screaming the word "Mohsen!"
The largely peaceful protest movement has been marked by actions including removing and burning headscarves in the streets, chanting anti-government slogans and confronting the security forces.
In a relatively new tactic, protest supporters staged three days of nationwide strikes up to Wednesday which closed down shops in major cities, according to rights groups.
The security forces have responded with a crackdown that has killed at least 458 people, including 63 children, according to an updated death toll issued by IHR on Wednesday.
A court on Tuesday sentenced five more people to death by hanging for killing a Basij member, bringing to 11 the number sentenced to death in connection with the protests.
Freedom of expression group Article 19 said urgent action was needed "as the lives of others on death row in relation to the uprising are in imminent danger".