United Nations Secretary-General Antonio Guterres appealed on Friday for Iranian security forces to refrain from using "unnecessary or disproportionate force" against anti-government protests triggered by the death of a woman in police custody.
He also urged everyone to exercise restraint to avoid further escalation, said Guterres' spokesman Stephane Dujarric.
"We are concerned about reports of peaceful protests being met with excessive use of force leading to dozens of deaths and injuries," Dujarric told reporters in New York. "We further call on the authorities to respect the right to freedoms of expression, peaceful assembly and association."
Guterres raised the issue of human rights with Iranian President Ebrahim Raisi on Thursday during a meeting between the pair on the sidelines of the annual gathering of world leaders at the United Nations, Dujarric said.
Iranians are fuming over the case of Mahsa Amini, 22, who died last week after being arrested by the morality police for wearing "unsuitable attire".
Guterres called for "a prompt, impartial and effective investigation by an independent competent authority" into Amini's death, Dujarric said.
The United Nations also urged the Iranian authorities to respect women's rights and implement effective measures to protect them from other human rights violations.
State-organised demonstrations took place in several Iranian cities on Friday to counter nationwide anti-government unrest, with marchers calling for the execution of protesters they termed "rioters."