TEHRAN — Iran's Intelligence Ministry said it arrested 11 people in connection with a deadly attack that killed scores of civilians on Wednesday in the city of Kerman, as crowds were commemorating slain commander Qasem Soleimani on the fourth anniversary of his killing by a US airstrike.

In a statement published by the state-run IRNA news agency on Friday, the ministry confirmed that those arrested individuals were involved in the "logistics and liaison" behind the attacks and were rounded up from across six provinces.

Claimed by the Islamic State (ISIS), the twin suicide blasts killed at least 89, among them children, and marked the deadliest-ever bombing attack in the 43-year history of the Islamic Republic.

According to Iranian officials, one of the assailants was of Tajik nationality, and work was being done to identify the second. The ISIS claim of responsibility was made public via the group's propaganda platforms more than 24 hours after the attack.

Both before and after the announcement, Iran's top officials, including President Ebrahim Raisi, blamed the "enemies" — the United States and Israel. "They are incapable of fighting back the resistance groups [in Gaza], thus taking the war on innocent people," he declared in a televised speech on Wednesday.

The Islamic Republic insists that ISIS was "created" and continues to be supported by the United States and Israel, an assertion which both countries have dismissed.

"The US and Israel were the main perpetrators, and they paid money to ISIS to shoulder responsibility," said ultraconservative cleric Ahmad Alamolhoda, one of the most influential clerics in Iran and a close ally of supreme leader Ali Khamenei, as he led Friday prayer sermons in the holy city of Mashhad.

Vague pledges for revenge

Iranian authorities have promised a "harsh" response, whose timing, place and nature will be their own choice. "Revenge is just the lowest price that the enemy will have to pay over the crime they committed," said Raisi when he met with the families of the victims on Thursday.

"Revenge, revenge!" demanded a crowd of hardliners in Kerman as they interrupted a speech by the chief of the Revolutionary Guards, Maj. Gen. Hossein Salami. Iranian officials made similar promises in the wake of Soleimani's death. Four years on, hard-line loyalists have grown increasingly disillusioned by the state's perceived failure to take proportional action against those involved in the killing of the influential commander.