Amir Hossein Hatami, 18, was sentenced to death in February along with six others by a Tehran revolutionary court and was hanged at dawn in the notorious Ghezel Hesar prison outside the capital, according to Norway-based NGO Iran Human Rights.

The Iranian judiciary's Mizan Online website said he acted "against national security" on behalf of Israel and the United States by breaking into "a military centre and destroying it in order to seize the weapons stored there" during the protests.

But Amnesty International said it was "outraged by the arbitrary execution of the teenage protester", adding the trial was "grossly unfair" and that he had been sentenced to death less than a month after his arrest.

Hatami is the fourth man to be executed over protests that broke out in Iran in late December against the rising cost of living before evolving into nationwide anti-government demonstrations. The protests peaked on January 8 and 9 and were met with a crackdown that activists say left thousands dead.

On March 19, authorities executed three men convicted of killing police in the protests, including 19-year-old Saleh Mohammadi, a wrestler who took part in international competitions.

This week, authorities have hanged four men convicted on charges of rebellion for membership in the banned People's Mujahedin of Iran (MEK) after their sentences were upheld by the supreme court.

Hatami "was subjected to torture and sentenced based on forced confessions in a grossly unfair trial before the revolutionary Court", said IHR director Mahmood Amiry-Moghaddam.

"In the past two weeks alone, three protesters and four political prisoners have been executed, and hundreds more remain at imminent risk," he added. IHR said that just 84 days had elapsed between his arrest and execution.

- 'Tool of repression' -

The seven were accused of setting fire to a base belonging to the Basij militia -- a volunteer force of the Revolutionary Guards -- in Tehran during the protests.

But defence lawyers accused plainclothes forces of trapping protesters inside a building, locking the doors, and themselves starting the fire.

Amnesty International said that the execution showed the judiciary is "a tool of repression sending individuals to the gallows to spread fear and exacting revenge on those demanding fundamental political change".

IHR said the seven men had been convicted in the fast track-trial -- just a month after their arrest -- by the court presided over by the notorious judge Abolqasem Salavati.

Salavati was sanctioned in 2019 by the United States, which said he is known as the "Judge of Death" for his frequent death sentences.

The executions came amid Iran's war with Israel and the United States which erupted on February 28 with strikes that killed the Islamic republic's supreme leader, Ali Khamenei.

"Hundreds more now face imminent executions in the coming days and weeks," warned Amiry-Moghaddam.