Human Rights Watch said thousands of people took to the streets last week in Iran to protest the detention of Iranian opposition leaders Mehdi Karroubi and Mir Hossein Mousavi.
The rights group said that in many cases, there were more security forces on the streets than protesters. Witnesses told Human Rights Watch that riot police were using tear gas, batons and birdshot to control the demonstrations.
"Iran should understand that its strong-arm tactics aren't impressing anyone," said Joe Stork, Middle East deputy director at Human Rights Watch, in a statement. "(Tehran) needs to call off the attackers and start prosecuting any member of security forces using unjustified force against protesters, regardless of rank or affiliation."
Human Rights Watch said at least three people were killed during February demonstrations in Iran. Iran denies the charges, blaming anti-government forces for the deaths.
Iranian lawmakers accused Karroubi and Mousavi of treason and earlier called for their execution.
Notable deaths of 2014 [PHOTOS]