The rights group condemned the deaths as evidence that Iran's security forces went "on a horrific killing spree." Iran has not provided an updated death toll of its own.
At least 208 people were killed in Iran during last month's protests over government-set gasoline price hikes and the subsequent security crackdown, Amnesty International said Monday.
"The number of people believed to have been killed during demonstrations in Iran that broke out on 15 November has risen to at least 208, based on credible reports received by the organization," said the rights group, adding that the actual death toll was likely higher.
The new figure increases the death toll by almost 50. Amnesty said dozens of those deaths were recorded in Shahriar city in Tehran province, "one of the cities with the highest death tolls."
The protests erupted on November 15 with the surprise announcement of a petrol price hike of 200%, but were quashed by authorities, who also imposed a weeklong internet blackout in the country.
The number of deaths is "evidence that Iran's security forces went on a horrific killing spree," said Philip Luther, Amnesty's research and advocacy head for the Middle East, and called on the international community to ensure those responsible are held accountable.
Authorities said as many as 200,000 people demonstrated last month, with some attacking banks, police stations and gas stations. The protests extended across 100 cities and towns in the country.
The rights group added that according to accounts it collected, "families of victims have been threatened and warned not to speak to the media, or to hold funeral ceremonies for their loved ones."
Iran has not yet released any nationwide figures over the widespread unrest, but confirmed five deaths. The state rejected Amnesty's previous numbers.
The speaker of the Iranian parliament, Ali Larijani, did not offer a new official death toll when asked at a news conference broadcast on Sunday.
"That some were injured in the recent incidents or had problems or people's properties were burnt or damaged... security bodies will certainly follow up and it is their responsibility to do so," he said.
Iran's constitution outlines protesting as a right, he continued, but that "the problem is where protests turn into violent behavior and some use firearms and cold weapons."
mmc/ng (AP, AFP)