TEHRAN, Iran -- Police increased their patrols in the streets and subway stations of Tehran on Thursday, a day after a pair of stunning ISIS-claimed attacks on Iran's parliament and the tomb of its revolutionary leader killed at least 17 people and wounded more than 40.

Five of the men who launched the attack in the heart of Iran's capital previously fought for the Islamic State of Iraq and Syria (ISIS), Iran's Intelligence Ministry said Thursday, acknowledging the first such assault by the Sunni Muslim extremists in the Shiite power.

The ministry issued a statement on its website with bloody pictures of the men's corpses. It identified them only by their first names, saying they didn't want to release their last names due to security and privacy concerns for their families.

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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 ISIS leader and escaped when authorities initially broke up their extremist cell.

The ministry did not identify the men's hometowns, nor say how they were able to evade authorities.

Commuters in the Iranian capital noticed police on street corners and motorcycles, more than usual 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.

The attack Wednesday as lawmakers held a session in parliament and at the shrine of Ayatollah Ruhollah Khomeini shocked Iranians who so far had avoided the bloodshed that has followed ISIS' rise in Iraq and Syria. Iranian forces are backing embattled Syrian President Bashar Assad while the Shiite power also is supporting militias fighting against the extremists in Iraq.

The bloodshed shocked the country and came as emboldened Sunni Arab states -- backed by U.S. 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 and thus bore some of the blame.

"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."

Repugnant WH statement & Senate sanctions as Iranians counter terror backed by US clients.Iranian people reject such US claims of friendship — Javad Zarif (@JZarif) June 8, 2017

The comments sparked anger from Iranian officials, and Iranian nationals on social media, who recalled the vigils in Tehran that followed the Sept. 11 attacks. Foreign Minister Mohammad Javad Zarif in a tweet on Thursday called the White House comments "repugnant" and accused the U.S. of supporting terror.

"Iranian people reject such U.S. claims of friendship," Zarif tweeted.

Iran's powerful Revolutionary Guard indirectly blamed Saudi Arabia for the attacks. A statement issued Wednesday evening stopped short of alleging direct Saudi involvement but called it "meaningful" that the attacks followed Trump's visit to Saudi Arabia, where he strongly asserted Washington's support for Riyadh.

The statement said Saudi Arabia "constantly supports" terrorists including ISIS, adding that the ISIS 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 told The Associated Press on Wednesday that "the Iranian government should not use the attack in a very polarized situation against Saudi Arabia or claim that Saudi Arabia is somehow linked to the attack, because it isn't."

Iranian state television reported the increase in the death toll to 16 on Thursday, citing Ahmad Shojaei, the head of the country's forensic center. He told state TV that "three of the victims are women." He did not elaborate.

Iranian authorities have said assailants were Iranian nationals, adding they have arrested six suspects, including one woman, since the attack Wednesday in Tehran.

On the streets of the capital 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 the King Salman and the kingdom's defense 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 destabilize 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 midmorning 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 slain 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. He did not elaborate.

Tehran's stock exchange fell nearly 2 percent Thursday after the attacks.