Measures to boost security along its borders with Afghanistan and Pakistan have been taken by Iran, in a first indication that it suspects Wednesday’s attack was the work of the Islamic State group (ISIS).

In yesterday’s attack, at least 84 people were killed when two explosions went off near the tomb of Qasem Soleimani in the southern city of Kerman, four years after he was killed in a US drone strike in Baghdad.

The border closure suggests Iran believes the attack may have begun from Islamic State – Khorasan Province, a Sunni group operating mainly in Afghanistan that blames Soleimani for inflicting heavy damage on the Islamic State in Iraq and Syria.

“We have points on the Afghan and Pakistani borders that are a priority for blockade,” Iran’s Interior Minister Ahmad Vahidi said on Thursday.

One of the main objectives will be to restrict the movement of those crossing the border, which will be discussed with the Taliban.

An Afghan opposition leader, Ahmad Masood, had already sent a condolence message to Iran in which he made it clear he believed the Islamic State was involved. The group was responsible for a previous deadly attack in Iran in 2017.

Earlier, Iran’s Foreign Minister Hossein Amir-Abdollahian said the country had sent a letter to the UN Security Council to inform its members that it was taking all “legal measures” to reveal who was responsible for the attack in Kerman.

The Revolutionary Guards promised a tough response, describing the attack as a “blind and vicious act”.