Thousands have turned out to mourn the victims of the Tehran attacks, shouting "Death to Saudi Arabia" and "Death to America." It comes after Iranian leaders accused Washington and Riyadh of supporting the attacks which killed 17 people earlier this week.

Crowds gathered on the streets of the Iranian capital to shout slogans against the US, Saudi Arabia, and Israel on Friday, while reaching out to touch coffins wrapped in flags and covered in flowers.

Earlier on Friday, Iran's supreme leader, Ayatollah Ali Khamenei, said the attacks would only increase Tehran's hatred against the US and its "stooges" including Saudi Arabia.

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)," he said ahead of the funeral, according to state media.

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During the funeral, Iranian parliament speaker Ali Larijani called the US the "international" version of Islamic State (IS, formerly ISIS/ISIL). He also accused Washington of exchanging democracy for money, referencing a massive arms deal recently agreed between the US and Saudi Arabia.

He went on to state that anti-Iranian remarks by Saudi Arabia's foreign minister and US President Donald Trump were a "matter of disgrace."

Larijani criticized a step by the US Senate to proceed with a new set of sanctions against Iran, including its elite Revolutionary Guards. The US decision was confirmed on the same day as the Tehran attacks.

The comments come just one day after Iran's intelligence minister, Mahmoud Alavai, said investigators were working to determine whether Riyadh had a role in Wednesday's attacks, but that it was too soon to reach a conclusion. However, Iran's Revolutionary Guards (IRGC) didn't waste any time blaming Saudi Arabia for the attacks.

"This terrorist attack happened only a week after the meeting between the US president (Donald Trump) and the (Saudi) backward leaders who support terrorists. The fact that Islamic State has claimed responsibility proves that they were involved in the brutal attack," a Wednesday statement from the Revolutionary Guards said, as quoted by Reuters.

IRGC Brigadier General Hossein Salami also vowed that Iran would "take revenge" for the attacks.

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“Let there be no doubt that we will take revenge for today's attacks in Tehran, on terrorists, their affiliates and their supporters,” he said on Wednesday, as quoted by Mehr news agency.

Saudi Arabia's foreign minister was quick to reject allegations that Riyadh was involved, saying on Wednesday that the country "condemns terrorist attacks anywhere they occur and we condemn the killing of the innocent anywhere it occurs."

Meanwhile, Iran's interior ministry said Friday that a total of 41 suspects linked to the attacks have been arrested.

"With the help of security forces and families of the suspects, 41 people linked to the attacks and to Daesh (Islamic State) have been arrested in different provinces," the ministry said, according to state TV cited by Reuters.

"Lots of documents and weaponry have been seized as well," it added.

The intelligence ministry also said forces stormed multiple "safe houses" linked to IS in northwest Iran, according to state media.

Two guards, 10 government staffers, and five civilians were killed in the Wednesday attacks which targeted the country's parliament and shrine of the late founder of Iran, Ayatollah Ruhollah Khomeini. Fifty-two others were injured in the attacks, according to the Interior Ministry. IS claimed responsibility for the assaults, and threatened more against Iran's Shiite majority.