Reports from Iran say police have increased patrols in the streets and subway stations of the capital, Tehran, as the death toll rose a day after attacks on parliament and Ayatollah Ruhollah Khomeini's shrine.
Iranian officials said on June 8 that 17 victims were killed and more than 40 wounded in the attacks a day earlier -- the first major attacks in Iran for which the extremist group Islamic State (IS) has claimed responsibility.
The Intelligence Ministry, meanwhile, said in a statement that five men involved in the attacks were Iranians who joined IS in Iraq and Syria.
The ministry released the first names of the men and published pictures of their corpses.
Describing them as "long affiliated with the Wahhabi" -- a reference to a conservative form of Sunni Islam dominant in Saudi Arabia -- it said the five had left Iran to fight for IS in Mosul, Iraq, as well as Raqqa, Syria
The ministry said the group returned to Iran in summer last year under the command of an IS leader to carry out terrorist operations in religious places, and escaped when authorities broke up their cell.
In the twin attacks that lasted several hours, officials said assailants armed with Kalashnikov rifles stormed the parliament building in central Tehran while another group of assailants targeted Khomeini's mausoleum.
All the attackers were reported killed. At least two of them blew themselves up with suicide vests, Iranian media reported.
Police say they arrested several suspects as part of their investigation into the attacks, while the Intelligence Ministry said on June 7 that members of a third "terrorist group" were arrested before being able to carry out any attack.
IS Claims Responsibility
Claiming responsibility for the attacks, IS released a video purporting to show gunmen inside parliament.
IS has regularly threatened Iran, which is backing militias battling IS fighters in both Iraq and Syria. The extremist Sunni group considers the 90 percent of Iranians who are Shi'ite Muslims to be apostates.
Releasing their first Persian-language video in March, IS militants threatened to step up recruitment within the country and threatened to "conquer Iran and restore it to the Sunni Muslim nation as it was before."
Iran's sizable Sunni minority population resides mostly in restive areas near the borders with Iraq and Pakistan.
Supreme Leader Ayatollah Ali Khamenei sought to play down the Tehran attacks, calling them mere "firecrackers" that would have no effect on "the will of the people."
President Hassan Rohani, a relative moderate who advocates engagement, said they would make Iran "more determined in the fight against regional terrorism, extremism, and violence," and called for international cooperation against the terror threat.
But Iran's Islamic Revolutionary Guards Corps (IRGC) took a harsh tone, vowing revenge for the bloodshed and pointing the finger at the United States and its ally Saudi Arabia.
Zarif Slams Washington
In a statement, the IRCG called it "meaningful" that the attacks followed President Donald Trump's visit to the Sunni-ruled kingdom, where he strongly asserted Washington's support for Riyadh.
Saudi Arabia, Iran’s staunch regional rival, "constantly supports" terrorists, it said, adding that the IS claim of responsibility “shows they are involved in this savage action."
Riyadh and the United States both condemned the attacks, which came as Saudi Arabia and other Sunni-ruled countries cut ties with Qatar over alleged support for Islamist militants and closer ties with Iran.
In a statement, Trump expressed sympathy for the victims of the Tehran attacks but also implied that Iran is itself a sponsor of terrorism, saying, "We underscore that states that sponsor terrorism risk falling victim to the evil they promote."
Iranian Foreign Minister Mohammad Javad Zarif took to Twitter to denounce Trump's reaction to the attacks and moves by U.S. lawmakers to slap new sanctions on Iran.
"Repugnant WH statement & Senate sanctions as Iranians counter terror backed by US clients. Iranian people reject such US claims of friendship,” said in a tweet.
The U.S. Senate advanced on June 7 a package of new sanctions on Iran to punish Tehran for its ballistic missile program, arms transfers, and support for militant groups in the Middle East.
Senators voted on a procedural measure that sets up a final vote in the coming days.
Before the vote, several senators had urged a delay, arguing that the timing was inappropriate because of the terrorist attacks in Tehran.
The bill would sanction people involved in Iran's ballistic missile program and anyone who does business with them.
The measure would also apply financial and other restrictions on the Revolutionary Guards and enforce an arms embargo.
With reporting by AP, AFP, and Reuters