Death toll in Iran crackdown exceeds 300, Amnesty says
The rights group had earlier estimated 208 deaths, including two youths aged 15 and 17.
Iran has dismissed such figures as "utter lies".
Amnesty said it collected "harrowing testimony" suggesting that after authorities "massacred" protesters, they orchestrated a "wide-scale clampdown" to cover up the deaths.
"Iran's authorities are carrying out a vicious crackdown following the outbreak of nationwide protests on 15 November," the London-based rights watchdog said in a statement.
"Thousands of protesters as well as journalists, human rights defenders and students" were arrested, Amnesty said, "to stop them from speaking out about Iran’s ruthless repression".
The nationwide demonstrations were triggered by a shock fuel price hike.
Authorities restored order within days, but so far have confirmed just five deaths, including four members of the security forces killed by "rioters".
An official death-toll based on figures from the national forensic institute is awaited.
"Independent sources" told Amnesty that a month after the unrest, "security forces are still carrying out raids across the country to arrest people in their homes and places of work."
Adolescents as young as 15 have been "detained alongside adults", Amnesty said.
With dozens held in "incommunicado detention" and others in "conditions amounting to enforced disappearance", some detention centres face "severe overcrowding", Amnesty claimed.
The organisation called on Tehran to "urgently and unconditionally release all those who have been arbitrarily detained".
It called on the international community to apply urgent pressure, without which "thousands will remain at risk of torture and other ill-treatment".
Earlier this month the United Nations said at least 7,000 people have "reportedly" been arrested in Iran since mass demonstrations erupted last month, and called for the immediate release of those arbitrarily detained.
In a statement, the UN human rights office also said it had obtained "verified video footage" showing security forces firing on protesters, apparently with intent to kill.
The rights office added that it had "information suggesting that at least 208 people were killed" during the unrest, supporting a toll previously given by Amnesty International.
"There are also reports, which the UN Human Rights Office has so far been unable to verify, suggesting more than twice that number killed," the statement added.
The UN High Commissioner for Human Rights, Michelle Bachelet, said video obtained by her office shows "severe violence was used against protesters.”
"We have also received footage which appears to show security forces shooting unarmed demonstrators from behind while they were running away, and shooting others directly in the face and vital organs – in other words shooting to kill," Bachelet said.
Additional video material shows "armed members of security forces shooting from the roof of a justice department building" in the city of Javanrud, west of Tehran in Kermanshah Province, as well as gunfire from helicopters in Sadra, in Fars Province.
Bachelet charged that "many of the arrested protesters have not had access to a lawyer," while raising alarm over "reports of severe overcrowding and harsh conditions in detention centres, which in some cities include military barracks, sports venues and schools."
"I urge the authorities to immediately release from detention all protesters who have been arbitrarily deprived of their liberty," she further said.
Iran has blamed the violence that broke out during the protests on "thugs" backed by its foes the United States, Israel and Saudi Arabia.