According to the Iranian authorities, a gunman stormed the Shah Cheragh shrine in Shiraz on Wednesday afternoon and martyred 15 people and wounded 19 more.
Fars Province's police commander has said that there was only a terrorist.
Security sources have said that the gunman was Takfiri-Wahabbi terrorist who abused the recent unrest in the country to carry out his attack.
Some sources are saying that the terrorist is not Iranian.
The news service of the Supreme National Security Council (SNSC) Nournews said that 15 have been martyred and around 40 were injured in the terrorist attack.
The attack targeted worshippers who were preparing for evening prayers. Reports say one woman and three children were among the victims.
The terrorist started shooting at the worshippers after entering the holy shrine through the front door.
The gunman has reportedly been arrested by the security forces.
Preliminary reports said there were three terrorists but the Fars province authorities later said there was only one terrorist.
Other reports say that an accomplice has been arrested near the shooting place.
The Fars governor, where Shiraz is located, has put the number of the wounded at 21.
In a message on Wednesday evining, the speaker of the parliament Mohammad Bagheri Ghalibaf emphasized that the security and law enforcement forces should take serious measures to identify the perpetrators behind the deadly incident in the Shah Cheragh shrine and that the medical centers should treat the injured in the best way possible.
Stéphane Dujarric, Spokesperson for the Secretary-General of the United Nations has offered Iran condolences over the terror attack.
The Iranian interior minister Ahmad Vahid has blamed the foreign enemies for inciting violence in the country and today's attack.
Iraq's Ammad Hakim has condemned the terrorist attack in Shiraz.
MNA