Five Tehran attackers had fought for IS, says Iran
Five of the men who launched an attack in the heart of Iran's capital previously fought for Islamic State, the country's intelligence ministry has said.
The attacks on Wednesday on Iran's parliament in Tehran and the tomb of its revolutionary leader killed at least 16 people and wounded more than 40.
The ministry issued a statement on its website with bloody pictures of the men's bodies.
It identified them only by their first names, saying it did not want to release their last names due to security and privacy concerns for their families.
It described them as "long affiliated with the Wahhabi", an ultraconservative form of Sunni Islam practised in Saudi Arabia.
However, it stopped short of directly blaming the kingdom for the attack, though many in the country expressed suspicion that Iran's regional rival had a hand in the attack.
The men had left Iran to fight for the extremist group in Mosul, Iraq, as well as Raqqa, Syria - the group's de facto capital, the ministry said.
It said they returned to Iran in August under the command of an IS leader and escaped when authorities initially broke up their extremist cell.
The ministry did not identify the men's home towns or say how they were able to evade authorities.
Commuters in the Iranian capital noticed more police than usual on the streets as dawn broke.
That came after Mohammad Hossein Zolfaghari, a deputy interior minister, told state TV that "law enforcement activities may increase".
"We are focused on intelligence" gathering, he said.
State television also reported on Thursday that the death toll had risen to 16, citing Ahmad Shojaei, the head of the country's forensic centre.
The attack as politicians held a session in parliament and at the shrine of Ayatollah Ruhollah Khomeini shocked Iranians, who so far had avoided the chaos that has followed IS's rise in Syria and Iraq.
Iranian forces are backing embattled Syrian president Bashar Assad while the Shiite power is also supporting militias fighting against the extremists in Iraq.
The attack came as emboldened Sunni Arab states - backed by US President Donald Trump - are hardening their stance against Shiite-ruled Iran.
The White House released a statement from Mr Trump condemning the terrorist attacks in Tehran and offering condolences, but also implying that Iran is itself a sponsor of terrorism.
"We grieve and pray for the innocent victims of the terrorist attacks in Iran, and for the Iranian people, who are going through such challenging times," the statement said.
"We underscore that states that sponsor terrorism risk falling victim to the evil they promote."
The comments sparked anger from Iranians on social media, who recalled the vigils in Tehran that followed the September 11 attacks.
Foreign minister Mohammad Javad Zarif called the White House comments "repugnant" and accused the US of supporting terror.
"Iranian people reject such US claims of friendship," Mr Zarif tweeted.
Iran's powerful Revolutionary Guard indirectly blamed Saudi Arabia for the attacks.
A statement issued on Wednesday evening stopped short of alleging direct Saudi involvement but called it "meaningful" that the attacks followed Mr Trump's visit to Saudi Arabia, where he strongly asserted Washington's support for Riyadh.
The statement said Saudi Arabia "constantly supports" terrorists including IS, adding that the IS claim of responsibility "reveals (Saudi Arabia's) hand in this barbaric action".
The "spilled blood of the innocent will not remain unavenged", the Revolutionary Guard statement said.
Emirati minister of state for foreign affairs Anwar Gargash said "the Iranian government should not use the attack in a very polarised situation against Saudi Arabia or claim that Saudi Arabia is somehow linked to the attack, because it isn't".
On the streets of the capital on Thursday, Iranians said they remained suspicious that Saudi Arabia had a hand in the attack.
Some pointed to comments in May by Saudi Deputy Crown Prince Prince Mohammed bin Salman, the son of King Salman and the kingdom's defence minister, who said his country would "work so that it becomes a battle for them in Iran and not in Saudi Arabia".
"I am sure Persian Gulf Arab countries are behind this," said Nahid Ghanbari, a 21-year-old university student studying accounting.
"They have been angry about Iran's power in the region. They look for a way to destabilise our country."
Ayatollah Ali Khamenei, the country's supreme leader, used the attacks to defend Tehran's involvement in wars abroad.
He told a group of students that if "Iran had not resisted" it would have faced even more troubles.
"The Iranian nation will go forward," he added.
The violence began in mid-morning when assailants with Kalashnikov rifles and explosives stormed the parliament complex where a legislative session had been in progress.
The siege lasted for hours and one of the attackers blew himself up inside, according to Iran's state TV.
Images circulating in Iranian media showed gunmen held rifles near the windows of the complex.
One showed a toddler being handed through a first-floor window to safety outside as an armed man looked on.
As the parliament attack unfolded, gunmen and suicide bombers also struck outside Khomeini's mausoleum on Tehran's southern outskirts.
Khomeini led the 1979 Islamic Revolution that toppled the Western-backed shah to become Iran's first supreme leader until his death in 1989.
Iran's state broadcaster said a security guard was killed at the tomb and that one of the attackers was killed by security guards. A woman was also arrested.
The revered shrine was not damaged.
Police on Thursday said they now held six suspects as part of their investigation into the attacks.
Reza Seifollahi, an official in the country's Supreme National Security Council, was quoted by Iranian media as saying that the perpetrators of the attacks were Iranian nationals.