London: Iran's Revolutionary Guard lashed out at Saudi Arabia on Wednesday, hours after at least 13 people were killed and 42 others were wounded in devastating attacks on two potent symbols in Tehran, the capital: Iran's Parliament and the mausoleum of Ayatollah Ruhollah Khomeini.

The Islamic State group immediately said it was behind the attacks, the first time that the Sunni Muslim extremist group has claimed responsibility for an assault in Iran, which is predominantly Shiite Muslim. The group, which views Shiite Muslims as apostates, is battling with Iranian-backed forces in Iraq and in Syria.

Iranian Foreign Minister Javad Zarif tweeted: "Terror-sponsoring despots threaten to bring the fight to our homeland. Proxies attack what their masters despise most: the seat of democracy."

He did not explicitly blame any country but the tweet appeared to refer to comments made by Saudi Arabia's deputy crown prince, Mohammed bin Salman al- Saud, in May, saying that Riyadh would bring "the battle" for regional influence to Iran.

Sunni Saudi Arabia denied any involvement in the attacks, but the assault further fuels tensions between Riyadh and Tehran as they vie for control of the Gulf and influence in the wider Islamic world. It comes days after Riyadh and other Sunni Muslim powers cut ties with Qatar, accusing it of backing Tehran and militant groups. That move came after a visit by US President Donald Trump.

Qatar is the one Persian Gulf country that maintains relations with Iran.

In a statement, the Islamic Revolutionary Guard Corps faulted both Saudi Arabia and the US government: "The public opinion of the world, especially Iran, recognises this terrorist attack - which took place a week after a joint meeting of the US president and the head of one of the region's backward governments, which constantly supports fundamentalist terrorists - as very significant," clearly referring to Saudi Arabia. The statement also acknowledged IS's claim of responsibility.

 IS threatened more against Iran's majority Shiite population, seen by the hardline Sunni militants as heretics.

The deputy head of Iran's National Security Council, Reza Seifollhai, told state TV late on Wednesday that the attackers were people from Iran who had joined IS. Iranian police said they had arrested five suspects

Supreme Leader Ayatollah Ali Khamenei said: "These fireworks have no effect on Iran. They will soon be eliminated."

"They are too small to affect the will of the Iranian nation and its officials," state TV quoted him saying.

Saudi Foreign Minister Adel al-Jubeir said he did not know who was responsible for the attacks and said there was no evidence Saudi extremists were involved.

Attackers dressed as women burst through Parliament's main entrance, deputy interior minister Mohammad Hossein Zolfaghari said, according to the Tasnim news agency. One of them detonated a suicide vest, he said.

Of the victims of the attacks, 11 died at the Parliament building, and one at the mausoleum. In addition, six assailants were killed: four at the Parliament, and two at the mausoleum. Five were men, and one of the mausoleum attackers was a woman.

The attacks unfolded over several hours, starting around 10.30am, when men armed with assault rifles and suicide vests - some of them dressed as women - descended on the Parliament building, killing at least one security guard, and wounding and kidnapping other people. 

The building has been undergoing renovations intended to enhance security, particularly at the entrance, but they have yet to be completed.

On a video released by the IS  propaganda agency Amaq a man purportedly inside the Parliament says in Arabic: "Oh God, thank you.. Do you think we will leave? No! We will remain, God willing."

Police helicopters circled over parliament, with snipers on its rooftop. Within five hours, four attackers were dead and the incident was over, Iranian media said.

"I was inside the parliament when shooting happened. Everyone was shocked and scared. I saw two men shooting randomly," said one journalist at the scene.

Soon after the assault on parliament began, a bomber detonated a suicide vest near the shrine of the Islamic Republic's revered founder, Ayatollah Khomeini, a few kilometres south of the city, Zolfaghari said.

New York Times, Reuters