Iran's Revolutionary Guards say Saudi Arabia was behind twin attacks in Tehran on Wednesday that killed at least 12 people and injured 43, a statement published by the Guards said.

The pair of devastating attacks hit two of Iran's most potent symbols: the national Parliament and the mausoleum of the Islamic Republic's founder, Ayatollah Ruhollah Khomeini.

The Islamic State immediately claimed responsibility; if that is found to be true, the attacks would be the terrorist group's first major assault within Iran's borders. Suspicions in Tehran were also directed at Saudi Arabia, Iran's nemesis in the region, which has been newly emboldened by a supportive visit from President Donald Trump last month.

"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," said the Guards' statement, published by Iranian media.

In the view of many in Iran, the Islamic State, also known as ISIS or ISIL, is inextricably linked to Saudi Arabia. Hamidreza Taraghi, a hard-line analyst with ties to Iran's supreme leader, Ayatollah Ali Khamenei, said, "ISIS ideologically, financially and logistically is fully supported and sponsored by Saudi Arabia."

"They are one and the same," he added.

The attacks on Wednesday followed a familiar pattern of Islamic State assaults hitting more than one location. Assailants armed with assault rifles and suicide vests descended on the Parliament and on the Khomeini mausoleum. Six attackers were killed: four at the Parliament, and two at the mausoleum.

At Parliament, the assailants men entered the Parliament building in central Tehran, killed at least one security guard, and wounded and kidnapped other people, the semi-official news agency Fars reported. The building has been undergoing renovations intended to enhance security, particularly at the entrance, but they have yet to be completed.

In a sign that elite security forces had encountered trouble containing the situation, one attacker left the Parliament an hour into the siege, then ran around shooting on Tehran's streets before returning to the building where at least one of the assailants blew himself up on the fourth floor as others continued shooting from the windows.

"I cannot talk, I'm stuck here and the situation is really dangerous, the shooting is continuing, we are surrounded and I cannot talk," an Iranian journalist, Ehsan Bodaghi, said by phone from inside the Parliament building, before the call was disconnected. Yelling and screaming could be heard in the background.

About the same time as the attack on Parliament, around 10 miles to the south, two assailants entered the west wing of the sprawling Khomeini mausoleum, a main destination for tourists and religious pilgrims. According to local news agencies, at least one attacker detonated explosives in the western entrance. Another was reported to have committed suicide by swallowing a cyanide pill.

Iranian state television broadcast news of the attack on Parliament after a regular report on a session in the building, followed by an item on the increasing prices of kindergartens.

The speaker of Parliament, Ali Larijani, tried to play down the attacks as a "minor incident," saying that "some cowardly terrorists" had infiltrated the legislative complex and vowing that "the security forces will definitely take serious measures against them."

The Islamic State released a graphic video showing a bloodied man lying on the ground in the Parliament while a gunman in the background shouted, "Thank God! Do you think that we are going to leave? We will remain here, God willing."

The first terrorist attacks in more than a decade in Tehran come just over two weeks after Trump, with Saudi Arabia and its allies, vowed to isolate Iran. Iran has dismissed those remarks, made at a summit meeting in Riyadh, the Saudi capital, as a scheme by Trump to sell weapons to Saudi Arabia. The Iranian foreign minister, Mohammad Javad Zarif, has even suggested that Trump was "milking" Saudi Arabia.

Iran and Saudi Arabia are the leading nations on the opposing sides of the Middle East split between Shiite and Sunni Islam. Iran has military advisers in Iraq and Syria, and it controls and finances militias in those countries and in Lebanon. Tehran also has some influence over the Houthis fighting the government in Yemen, and it often speaks out in support of Shiites in Bahrain, a majority group that Iran says is repressed by the Sunni monarchy.

Saudi Arabia recently raised the volume of criticism against Iran, and the country led a regional effort on Monday to isolate Qatar, the one Persian Gulf country that maintains relations with Tehran.

Iran has long accused Saudi Arabia of supporting terrorists in the region, saying the kingdom had facilitated the rise of Sunni extremist groups such as the Islamic State and others in Iraq and Syria.

After Egypt, Saudi Arabia, the United Arab Emirates and other states cut ties with the gas-rich kingdom of Qatar, citing its support for Iran, Tehran rushed to fill the void, offering to ship food and medicine to Qatar.

"The Saudis feel empowered now," said Taraghi, the hard-line analyst. "They are now taking revenge in Tehran," he said, adding that Iran's policy was to drive a wedge between those in the Saudi alliance. "We are now helping Qatar," he said. "This Saudi alliance means nothing."

New York Times