Four gunmen burst into Tehran's parliament complex with rifles and a pistol, and one of the attackers blew himself up on the fourth floor, the semi-official ISNA news agency reported, putting the death toll at three.
IS claimed the attacks in a report from its Amaq propaganda agency which said: "Fighters from the Islamic State attacked the Khomeini mausoleum and the parliament building in Tehran". The militants are at war with Iranian-backed forces in Syria and Iraq, and view Shiites as apostates.
Gunmen stormed two major sites in the Iranian capital Wednesday, opening fire and detonating suicide blasts in parliament and at the revered tomb of the nation's Islamic revolution leader.
The two attacks, which wounded dozens of people, are likely to deepen enmity and the regional battle for power between Saudi Arabia and Iran.
"I was inside the parliament when shooting happened". Images of the blast were shown on Press TV, which said one assailant was shot dead before he could set off his explosives, but another succeeded in detonating a bomb.
Shortly after, a similar attack took place at the mausoleum of the Ayatollah Khomeini, leaving several persons injured.
Attacks are highly rare in Tehran and other major cities though a Sunni militant group named Jundallah and its splinter group Ansar al Furqan have been waging a deadly insurgency, mostly in more remote areas, for nearly a decade.
World leaders reaffirm commitment to fighting climate change
Under the deal, the United States had agreed to cut greenhouse gas emissions as much as 28 percent below 2005 levels by 2025. United States withdrawing from it is certainly bad news as the country is the second largest emitter of greenhouse gases.
The Islamic State group claimed the attack, marking the first time it has taken responsibility for an assault in Iran.
It said one of the attackers there was killed by security guards and a woman was arrested.
Gun ownership is tightly controlled in Iran, meaning those who carried out the attacks on the parliament and the shrine likely had to smuggle their weapons into the country. As Iran's first supreme leader, Khomeini is a towering figure in the country and was its revolutionary leader in the 1979 ousting of the shah.
In another statement the news agency said the attacks on Khomeini's shrine were carried out by two suicide bombers. The parliament building, with a green marble chamber for lawmakers, is in the center of the city, and the tomb complex for Ayatollah Ruhollah Khomeini is about 12 miles to the south near the global airport.
The attackers were holding a number of hostages inside the highly-fortified parliament building, Press TV reported, as Iranian officials scrambled to establish who was behind the attacks or whether they were coordinated.
Militant groups are also known to operate in Iran s southeastern Sistan-Baluchistan province, which borders Pakistan and has a large Sunni community.