In the wake of two deadly terrorist attacks that targeted the Iranian Parliament and the Imam Khomeini Mausoleum in Tehran, security sources have pointed to Iranian Kurds affiliated with ISIS as the likely perpetrators. While Iranian authorities arrested 41 people in connection to the attacks on Friday, only one attacker, Serias Sadeghi, has been identified. Sadeghi is an Iranian Kurd from Paveh, a city in western Iran, and has been cited as a prominent recruiter for ISIS in Iranian Kurdistan.

Wednesday’s attacks occurred simultaneously at around 10:30 a.m. during the middle of Ramadan, an annual, month-long observance among Muslims that commemorates the first revelation of the prophet Muhammad. It is not uncommon for ISIS to carry out attacks at this time, as militants seek “the honor of obtaining martyrdom” during “the holy month of jihad.” In the first attack, a team of four people carrying assault rifles and wearing suicide vests attempted to enter the administrative building of the Iranian Parliament. The attackers shot at some and kidnapped others, with one attacker running loose on the streets of Tehran. Eventually, one of the attackers detonated his vest, while the remaining three were killed in a shoot-out with police officers.

The second attack consisted of two people entering the Imam Khomeini Mausoleum, a tribute to the founder of the Islamic Republic that houses the remains of numerous political figures. In a nearly-identical scenario, one of the attackers, a female suicide bomber, blew up her vest, while the other was killed in a shoot-out. On Wednesday, The Guardian’s Simon Tisdall provided an analogy to explain the significance of the attack. For Iranians, he said, “the attack on Khomeini’s tomb is the equivalent of somebody trying to blow up the Lincoln Memorial in Washington, D.C.”

In total, at least 12 people were killed and 46 wounded. In a video posted Thursday on Amaq News, the ISIS media channel, five men and their leader, who some believe to be Sadeghi, claimed responsibility for both attacks. The men can be heard speaking in Arabic and Kurdish, lending credence to the all-but-confirmed theory that Iranian Kurds were behind the incident. “This is a message from the soldiers of Islamic State in Iran, soldiers of the first brigade of Islamic State in Iran which, God willing, won’t be the last,” the leader in the video says. “This brigade will mark the start of jihad in Iran, and we call on our Muslim brothers to join us.”

While the attacks represent ISIS’s first strike inside Iran, the nation has long been a suspected target of the Islamic State. In March, the group released a video saying they would “conquer Iran and restore it to the Sunni Muslim nation as it was before.” The majority of Iranian citizens are Shiites, whom ISIS regards as apostates. ISIS, on the other hand, subscribes to a strict version of Sunni Islam that comprises a mere five percent of Iran’s population. The fact that Wednesday’s attackers were most likely Sunni Iranian Kurds could signal the beginning of a larger insurgency within the nation. Indeed, that seems to be ISIS’s very goal. On Friday, Mashallah Shamsolvaezin, an Arabic affairs analyst, told The New York Times that “the border towns and villages and tribes along Iran’s east, west, and southern borders are poor and vulnerable to extremism,” with  “young unemployed men” particularly susceptible to recruitment.

Even with ISIS claiming responsibility for the attacks, Iranian officials have been quick to blame the incident on their international rivals: Saudi Arabia, Israel, and the U.S. On Friday, Iran’s supreme leader, Ayatollah Ali Khamenei, said the attacks would “only increase hatred for the governments of the United States and their stooges in the region like the Saudis.” While the White House said it was “grieving and praying” over the victims of the attacks, it scornfully noted that “states that sponsor terrorism risk falling victim to the evil they promote.” In a Thursday tweet, Iran’s foreign minister, Mohammad Javad Zarif, called the statement “repugnant,” arguing that the terrorist incident was “backed by U.S. clients.” “Iranian people reject such U.S. claims of friendship,” he added.

This sentiment was shared by a number of Iranians during the nation’s prayers on Friday. The Times reports that Friday worshippers shouted “Death to Saudi Arabia” and “Death the United States, Britain, and Israel.” Meanwhile, a speaker proclaimed that “America and Saudi Arabia could not get anything from their proxy wars, so they decided to bring the war here, inside Iran.” But the problem at stake remains even bigger than this deep-seated international rivalry: In their video released Thursday, ISIS suggested that Saudi Arabia could be next.