The deadly attack comes amid some of the largest protests to sweep Iran in recent years.
Iranian authorities on Wednesday said a terror attack on a shrine in the city of Shiraz killed at least 15 people, including several women and children.
So-called "Islamic State" (IS) claimed responsibility for the attack while Tehran said two men had been arrested and another was on the run.
The attack on the Shah Cheragh Mosque — one of the holiest sites in Iran — was carried out on the same day as Iranian security forces fired on protesters who had gathered at the grave of Jina Mahsa Amini.
What do we know about the attack?
IS reported the attack on its Amaq news agency, saying that an armed militant had opened fire at the shrine, claiming to have killed 20 people.
The semi-official Tasnim news agency reported that the assailant first shot dead an employee of the shrine before being chased by onlookers. His gun became jammed, but he was able to fix it before firing on his pursuers, the agency reported.
State media said the gunman wasn't Iranian, without specifying his nationality.
Iranian state TV blamed the attack on "takfiris" — the name given to ultraconservative Sunni Muslim extremists such as those belonging to IS. Iran is a Shiite majority country but has been spared much of the ethnic bloodshed seen in Iraq and Afghanistan where Shiites have often been targeted.A similar attack last April, however, saw a man stab two clerics to death at the Imam Reza shrine in the city of Mashhad.