(Reuters) - Protests raged for a fourth straight day across Iran on Tuesday and authorities said three people had been killed during unrest over the death of a young woman in police custody.

The death last week of 22-year-old Mahsa Amini who was arrested by morality police for "unsuitable attire" unleashed a flood of simmering anger over numerous issues including rights, security and an economy reeling from international sanctions.

It is some of Iran's worst unrest since street clashes last year over water shortages. The Iranian government accuses foreign agents and unspecified terrorists of instigating the violence.

In an apparent effort to defuse tensions, an aide to Iran's Supreme Leader Ayatollah Ali Khamenei paid condolences to Amini's family, saying that Khamenei was affected and pained by her death.

"All institutions will take action to defend the rights that were violated," Khamenei's representative in the Kurdistan province, Abdolreza Pourzahabi, said while visiting Amini's family home in Kurdistan province, state media reported.

"As I promised to the family of Ms. Amini, I will also follow up the issue of her death until the final result," Pourzahabi said.

Amini fell into a coma and died while waiting with other women held by the morality police, who enforce strict rules in the Islamic Republic requiring women to cover their hair and wear loose-fitting clothes in public.

Her father said she had no health problems and that she suffered bruises to her legs in custody and holds the police responsible for her death.

Demonstrations broke out in Kurdistan and spread on Monday and Tuesday to several other provinces in northwestern Iran.

Late on Tuesday state media reported "limited rallies" in several cities where it said demonstrators chanted anti-government slogans, threw rocks at police vehicles and damaged public property.

Videos posted on social media websites on Tuesday purported to show demonstrations in provinces across Iran, including several regions that had so far been untouched by the unrest.

Reuters could not independently verify those videos.

The deadliest unrest has taken place in the Kurdistan region, where state officials and activist websites have reported at least three people killed.

Newspapers with Amini, a victim of country's "morality police", are seen in Tehran

An undated picture obtained from social media shows Mahsa Amini

People protest outside Tehran's Amirkabir University of Technology following death of a woman in custody, in Tehran, Iran September 19, 2022 in this still image taken from a video obtained by REUTERS.

Kurdish human rights group Hengaw said the three people who died were killed n Monday when security forces opened fire.

The governor of Kurdistan province said the deaths were suspicious and blamed unspecified terrorist groups.

"A citizen of (the city of) Divandarreh was killed with a weapon that isn't used by the armed forces. Terrorist groups are looking to kill," Esmail Zarei Koosha said in comments reported by the semi-official Fars news agency.

Tehran Governor Mohsen Mansouri accused foreign agents of fomenting the violence in the country's capital. He said citizens of three foreign countries were arrested during gatherings overnight.