The country's Supreme Leader said the attacks will add to the hatred that Iranians harbor toward the US and Saudi Arabia.
In a condolence message ahead of a funeral for the victims, Ayatollah Ali Khamenei said the attack: "will not damage the Iranian nation's determination and the obvious result is nothing except an increase in hate for the governments of the United States and their stooges in the region like Saudi (Arabia)," state media reported.
The Islamic State group has claimed responsibility for the attacks. The IS media arm Aamaq released a video Thursday evening showing what it claimed was a message from the Tehran attackers. The four-minute video shows three masked men sitting on a floor holding automatic rifles.
One of the men speaks in the sorani Kurdish dialect common among Kurds in northeastern Iraq and northwestern Iran. The speaker claims to represent the "first battalion" of IS formed inside of Iran. He speaks out at length against Shiites and promises further attacks.
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State TV broadcast the ceremony live. He said anti- Iranian remarks by Saudi Arabia's foreign minister and US President Donald Trump are a "matter of disgrace" for them. Larijani also criticised a Wednesday decision by the US.
Senate to move forward on a new set of sanctions against Iran, including its elite Revolutionary Guards, a move that came on the same day as the Tehran attacks.
The Vatican today sent a message of condolence for the victims of the attack.
Pope Francis "laments this senseless and grave act of violence," and "assures the people of Iran of his prayers for peace," the message read.
As the funerals took place, Iranian authorities continued a widening crackdown. Iranian state TV said the Intelligence Ministry had detained 41 suspects in Tehran and the western Kurdish provinces of the country.
The report called the detainees "elements of the Wahhabi IS group," and said they were involved in operations, communication and logistics for the local Islamic State cell.