Kerman, Iran - The Islamic State group said Thursday that it carried out twin bombings which killed at least 84 people at a memorial ceremony in Iran for slain Revolutionary Guards general Qasem Soleimani.

The claim from IS came as Iran observed a day of national mourning for those killed in Wednesday's blasts.

In a statement on Telegram, IS said two of its members "activated their explosives vests" among the crowds who had come to honor Soleimani on the anniversary of his death in a targeted US drone strike in Baghdad four years ago.

Iranian investigators had already confirmed that the first blast at least was the work of a "suicide bomber" and believed the trigger for the second was "very probably another suicide bomber", the official IRNA news agency reported earlier, citing an "informed source".

The Security Council condemned the twin bombings as a "cowardly terrorist attack" and urged all UN member states "to cooperate actively" with Iran in holding its "perpetrators, organizers, financiers, and sponsors" accountable.

Soleimani, who headed the Guards' foreign operations arm the Quds Force, was a staunch enemy of IS, the Sunni extremist group which has carried out previous attacks in majority-Shiite Iran.

The death toll was revised down from around 100 the day after the bombings, which also wounded hundreds near Soleimani's tomb in the southern city of Kerman.

Iran has suffered deadly attacks in the past from jihadists and other militants, as well as targeted assassinations of officials and nuclear scientists committed by Israel.

Regional tensions have surged amid the Gaza war, and Iranian officials had initially blamed Israel for the bombings.

On Thursday, Interior Minister Ahmad Vahidi spoke to ISNA news agency about bolstering security over its porous borders with Afghanistan and Pakistan.

He said authorities have identified "priority points to block along the border" with the two countries, which has long been a key access point for militant groups, drug smugglers and irregular migrants.

Mass protests in response to the attacks have been called for Friday.

The dead will be buried in private funerals organized by their families, Tasnim news agency reported, citing the governor of Kerman.

Iran's emergency services chief Jafar Miadfar said 284 people were wounded in the bombings and "195 are still hospitalized."