On Thursday, former reformist Iranian President Mohammad Khatami condemned the terrorist attack in Shiraz, as well as violence in all its forms.

Khatami pointed out that "the terrorist operation shows how calamitous and merciless violence can be," and offered condolences to all the people who lost loved ones as a result of the attack.

He added that "the demand for a good, safe and just life is a natural request. If the people find that these conditions are not available, they have the right to criticize and protest." However, he stressed that "criticism and protest must negate violence and not be contaminated by it, especially in situations where Iran's enemies on the outside have false hope through inhumane weapons, such as sanctions or encouraging violence to exploit the pure blood of the country's youth."

Earlier, Iranian President Ebrahim Raisi stated that the Islamic Republic will deliver a crushing response to those responsible for the Wednesday terrorist attack on the holy shrine of Shah Cheragh in Shiraz, Iran's southwestern city.

The Iranian President affirmed that “the country’s security and law enforcement forces, having identified the root causes of this heinous crime, will deliver a decisive response to its architects and operatives," adding that this move is one that Iran's enemies committed out of desperation in order to harm Iran's united people.

Raisi also expressed his heartfelt condolences for the pilgrims who died during the Wednesday massacre.

ISIS claimed responsibility on Wednesday for the attack on the shrine, which left 15 killed and 40 wounded.

Read more: Iran today stands stronger than ever: Raisi