Tehran hit out at Washington and Riyadh as tens of thousands attended the funerals Friday for those slain in the first attacks in Iran claimed by the Islamic State group.

The intelligence ministry, meanwhile, said Friday that 41 people suspected of being "agents of Daesh (IS)" had been arrested in the aftermath of Wednesday's attacks.

"Death to America", "Death to the Saud" ruling family, and "We are not afraid", shouted the crowd behind a lorry bearing the coffins of 15 of the 17 people killed.

Burials were held in the provinces for the two others killed when gunmen and suicide bombers stormed Tehran's parliament complex and the shrine of revolutionary leader Ayatollah Ruhollah Khomeini. Fifty people were wounded.

Supreme leader Ayatollah Ali Khamenei had initially called the attacks "firecrackers" that "will not have the slightest effect on the will of the people".

But on Friday, he turned his wrath over the attacks on the United States and Saudi Arabia, Iran's fiercest rivals.

"Such acts will have no other result than to reinforce hatred for the US government and its agents in the region, like the Saudi (government)," Khamenei wrote in a message of condolence.

At a ceremony held in parliament, attended by newly re-elected moderate President Hassan Rouhani, speaker Ali Larijani also attacked the United States and Saudi Arabia.

- US 'alignment with terrorists' -

He called regional rival Saudi Arabia "a tribal state very far from anything like a democracy", and denounced US sanctions against Iran over its ballistic missile programme.

The US "knows that the Revolutionary Guard and its Quds force are the most important regional forces fighting terrorists", Larijani said.

The imposition of such sanctions "demonstrates their alignment with terrorists in the region", said the speaker, a moderate conservative.

After prayers at Tehran University, a long procession left central Tehran for Behesht-e-Zahra cemetery near the Khomeini mausoleum, 20 kilometres (12 miles) away.

The attacks on two of Iran's most symbolic landmarks were carried out by five armed men, including suicide bombers who blew themselves up.

The intelligence ministry said they were Iranians who had joined the Islamic State group and travelled to its strongholds in Iraq and Syria before returning home.

Iran is a key fighting force against IS and other groups in Iraq and Syria, and the Sunni jihadists consider Shiite Muslims to be apostates.

Shiites make up roughly 90 percent of Iran's population, but the country also has a sizeable Sunni minority, particularly around its restive borders with Iraq and Pakistan.

IS released a video overnight of the five attackers before the assault, via its Amaq propaganda agency.

- Attackers in new video -

"Allah permitting, this is the first brigade that was established (in Iran) but it will not be the last," one said, as the group sat masked in a circle with their weapons.

The jihadist group had earlier released footage of the attackers from inside the building, also via Amaq -- a rare claim of responsibility while an assault was still going on.

Although the US military is also fighting IS in Syria, as well as Iraq, President Donald Trump said in response to the attacks in Iran that the country is reaping what it sows.

That drew fire from Iran's foreign minister, Mohammad Javad Zarif, who tweeted: "Repugnant WH (White House) statement... as Iranians counter terror backed by US clients."

Since Trump took office in January, relations between Washington and Tehran have worsened.

Washington has imposed new sanctions on Tehran for its alleged support of "terrorist" groups in the Middle East, ballistic missile tests and human rights abuses.

On a recent trip to Sunni-ruled Saudi Arabia, Trump called on all nations to "isolate" Iran.

The Islamic republic's elite Revolutionary Guard has accused Saudi Arabia of involvement in Wednesday's attacks.

But Intelligence Minister Mahmoud Alavi has said "we still cannot judge that Saudi Arabia has had a role in this terrorist incident".

On Friday, his ministry said 41 suspected IS "agents" were arrested after the attacks in Tehran and in the northwestern provinces of Kermanshah, Kurdistan, and West Azerbaijan, near the borders with Iraq and Turkey.

Documents and equipment "for carrying out terrorist operations" were seized, it said.

A nationwide hunt has uncovered explosive vests and other equipment, as well as an abandoned car containing at least 22 pistols, in Kermanshah province.

The Mizanonline website, which is close to the judiciary, earlier reported nine arrests.

Source: AFP