Iran has executed two men found guilty of killing a pro-regime militia member during anti-government protests, official media have reported.
The UK, calling the executions “abhorrent”, has led condemnation from western nations and human rights groups.
They are the third and fourth Iranians known to have been executed on charges relating to the months-long protests against the clerical regime.
The demonstrations were sparked by the death in custody of Mahsa Amini, 22, a woman arrested for allegedly breaking the country's strict dress code for women.
“Mohammad Mahdi Karami and Seyyed Mohammad Hosseini, the main perpetrators of the crime that led to the martyrdom of Ruhollah Ajamian, were hanged this morning,” the judicial news agency Mizan Online said.
Mizan said the officer was a member of the Basij paramilitary force and was killed in the city of Karaj, near Tehran, on November 3.
The Basij, a volunteer force of Iran's Islamic Revolutionary Guard Corps, have been used against protesters in major cities, attacking and detaining demonstrators.
Activists say at least 16 people have been sentenced to death in closed-door trials over charges linked to the protests. Death sentences in Iran are typically carried out by hanging.
“Iran must immediately end the violence against its own people,” UK Foreign Secretary James Cleverly said.
“The execution of Mohammad Mahdi Karami and Seyyed Mohammad Hosseini by the Iranian regime is abhorrent. The UK is strongly opposed to the death penalty in all circumstances.”
The UN human rights office said the executions followed “unfair trials based on forced confessions”.
A representative for EU foreign affairs chief Josep Borrell said the executions were "another sign of the Iranian authorities' violent repression of civilian demonstrations".
“The European Union calls once again on the Iranian authorities to immediately end the strongly condemnable practice of imposing and carrying out death sentences against protesters,” he added.
France's Foreign Ministry called the executions “revolting” and Germany said they “strengthen us in our desire to raise the pressure further on Tehran with the EU”.
The US-based Centre for Human Rights in Iran called on countries to withdraw their ambassadors from Tehran.
Protests led by women
At least 517 protesters have been killed and more than 19,200 people have been arrested, according to Human Rights Activists in Iran, a group that has closely monitored the unrest.
The Iranian authorities have provided varying death tolls that include protesters as well as members of the security forces. They have not released figures on the number of people arrested.
The protests began in mid-September after Ms Amini died days after being arrested in Tehran by Iran’s morality police.
Women have since played a leading role in the protests, with many publicly removing the compulsory headscarf in a show of defiance against the authorities.
The protests are one of the biggest challenges to Iran’s theocracy since the 1979 Islamic Revolution. The security forces have used live ammunition, bird shot, teargas and batons to disperse protesters, according to rights groups.