The United Nations Human Rights Council has decided to establish an independent mission to probe Iran's alleged suppression of ongoing mass protests.

In a special session in Geneva on Thursday, the UN council voted on a resolution to set up the investigative mission.

The resolution was adopted, backed by 25 countries of the 47-member-state council.

The public anger in Iran was sparked by the death of 22-year-old Mahsa Amini, who was arrested for allegedly improperly wearing her hijab headscarf. Her death has led to protests across Iran for more than two months.

The UN and human rights groups say Iranian security authorities have been cracking down on demonstrators, killing more than 300 people.

UN High Commissioner for Human Rights Volker Turk said the situation is unacceptable and Iran's investigations have failed to meet international standards of impartiality, independence and transparency.

The resolution says Iranian security authorities are unjustly detaining demonstrators and using sexual violence. It says the new fact-finding mission will submit a report on the situation in Iran to the UN.

China and some other nations opposed the resolution. They say human rights should not be used as tools to interfere with other nations. The representative from Iran said Tehran rejects the resolution as it is "based on lies."