On May 13, 2014, a pickup truck approached a caravan of white vans moving on a road near Baqubah, east of Baghdad, in Iraq. Within few meters of the caravan, the pickup exploded, leaving five Iranian engineers and several of their Iraqi guards dead, according to local news reports. The attack came less than 24 hours after a threat by ISIS spokesperson, Abu Mohammad al Adnani.

ISIS could—and very much wanted to—“transform Iran into pools of blood,” Adnani said. After all, Iran was the “bitterest enemy” of the Islamic State.

But al Qaeda long has been known to have deep, complex relations with Iran. And so ISIS, which grew out of a branch of al Qaeda in Iraq, “held back its soldiers and repressed its rage over the years to preserve the unity” of al Qaeda’s ranks.

“So let history record that Iran owes an invaluable debt to al Qaeda,” he added.

But in May, Adnani announced a change of plans: ISIS would not respect al Qaeda requests any more. And while Adnani did not overtly threaten Iran, the May 13th attack turned out to be one in a string of purported terror attacks against Iran and Iranians. These attacks have been pinned by local media and Iranian officials to ISIS and other Sunni extremist groups.

The American intelligence community has heard the claims. But they’re not sure whether the violence can be blamed on the Islamic State—or some other Sunni militants. “While no one is ruling out the possibility of an ISIL presence in Iran,” a U.S. intelligence official told The Daily Beast, using the government’s preferred acronym for ISIS, “at this time we are not able to validate reports of any activity there.”

ISIS’s rampage through Iraq has produced collateral damage that’s been largely unnoticed in the West. Iran, on the other hand, has been paying close attention. When ISIS took over the city of Jalawlah near the Iranian border, several Iranian media outlets reported a heavy attack on a border guard post near the city of Qasr-e-Shirin—on Iranian soil. The initial toll was reported four guardsmen killed in the incident. Qasr-e-Shirin’s representative in the Iranian parliament, a hardliner conservative named Fathollah Husseini, denied any casualties. But less than two days later, Iranian media outlets reported on funerals held for privates killed in the incident. Later reports suggested at least 11 Iranian border guards were killed in the incident.

Iranian political and military leaders tend to censor terrorist threats inside Iran, to bolster their reign over the country. But the ISIS threat is so bold inside Iran that even the highest officials have publicly acknowledged it. MohamdReza Rahmani Fazli, the Iranian interior minister and the highest ranking government official in charge of coordinating police and security efforts inside Iran, issued a warning on September 7 saying “Daesh”—a pejorative term for ISIS—“is posed to attack Iran imminently.”

Perhaps. But don’t expect a full-out ISIS invasion. After the extremist group took the Iraqi city of Tikrit in early July 2014, the majority of ISIS’s efforts have been concentrated on consolidating its power and eliminating pockets of resistance inside its territory. Evidently, ISIS’s current strategy is to launch guerrilla attacks and not a full invasion of Iran’s border regions. Given the history of arrangements of Iranians with sunni extremist militia that directly threatened Iran (as noted by Abu Mohamad Al Adnani), such attacks could push Iran to dial back its support for the Iraqi army and force Iran to accept ISIS’s presence in Sunni-populated regions of Iraq.

On the August 28, Jihadi twitter accounts associated with ISIS reported clashes of Islamic State sympathizers with Iranian Revolutionary Guard Corps units near the city of Urmia in West Azarbaijan providence. Iranian news outlets claimed that the attack was carried by ISIS, but no casualties were reported. The results of another strike, not far away, were quite different. On October 2, independent sources reported another ISIS attack near Khoi city, close to Urmia. The attack was an assassination which targeted an IRGC Sargent. Thousands attended the funeral of Sargent Mostafa Mohammad-Nezhad in Urmia on October 3.

In response, Iran has carried out mass arrests at home—and backed a series of offensives against ISIS abroad. On October, Iranian Minester of Intelligence Mahmoud Alavi was summoned by Iranian parliament to report on the latest developments around Sunni extremist groups in Iran. “As a result of tens of intelligence operations, more than 130 individuals believed to be key members of Takfiri [infidel] groups were arrested in past few months,” Alavi reported, using a pejorative term commonly attached to ISIS and other Sunni extremist outfits.

These arrests, Alavi claimed, were the result of a five-month long intelligence efforts which foiled at least four suicidal attack in Tehran—including a suicide bombing which targeted a massive demonstration in Tehran in late July.

Iran’s support for the Iraqi army—and Shi’a militias inside Iraq—is also putting a great deal of pressure on ISIS. On August 31, U.S. warplanes delivered at least four air strikes in support of Shi’a militia operations in the Iraqi village of Amirli. Later reports revealed that the operation in fact was led by notorious commander of the IRGC’s Qods Force, Maj. Gen.Qassem Suleimani.

Early on October 6, Iraqi army and Shi’a militia units operating in Anbar Providence identified a meeting of a half-dozen or more senior ISIS field commanders. According to Iraqi Army Lt. Gen. Rashid Falih, the location of the meeting place were passed to allied forces and three air strikes were carried “immediately” to the given coordinates. However, the results of that particular strike were not clear, The methodology suggests that Iraqi officers are probably mediating between allied officers and their Iranian and Iranian-led counterparts.

ISIS and its sympathizers have begun to open up a wide front against Iran, according to local media accounts. The group not only has demonstrated its presence in Iran’s Shi’ite west and north, closer to Iraq and Turkey. ISIS is also beginning to make its presence felt in long-troubled and mostly Sunni-populated eastern Iran. In early September 2014 residence of Mashhad city in northeastern iran reported graffiti hailing ISIS. The tags were signed by an unknown group calling itself the “Khorasan Division.” At the same time, the Tasnim news agency, run by the IRGC, reported that ISIS is sending propaganda via text message inside Iran. One of the texts: a claim that the Iranian government had poisoned Dates in southern Iran to kill Iran’s Arab minority.

While the threat of Sunni extremism influenced by ISIS success is increasing, the Iranian military’s front lines have appeared to be unreliable in the eastern part of the country. An attack in early September by a Sunni jihadist group called Jaysh Al Adl overran a border post called Eskan in a matter of minutes. JAA attack was executed “ISIS-Style.” 26 armed pick-up trucks, known as “technicals,” carrying 150 fighters were reportedly involved in the attack.

According Jaysh Al Adl, the attack started midnight when JAA fighters opened suppressive fire on the post and destroyed a BMP-2 armored vehicle inside. Then a suicide bomber drove a car to the post’s gate to cause a breach. To his astonishment, the driver found the gate open; guards already had abounded the border post. The driver parked the car near another BMP armored vehicle, ran away and then detonated 600 kilograms of explosive via a remote detonator. Backup forces rushed to the scene, but the JAA was ready. On the roads leading to the post, JAA fighters ambushed a quick response team, killing at least one IRGC officer.

JAA claims it have killed 30 IRGC officers in the raid, but there is no evidence supporting that claim. Nonetheless, the severity of the incident is appalling—especially given Iran’s recent history of trying to stop such strikes. In past 10 months, southeastern Iran has seen several brutal attacks from JAA. One attack in November 2013 killed 17 Iranian border guards; another in March 2014 captured five soldiers alive. In May, the IRGC declared that it was taking over responsibility of border police and is reinforcing border posts. It was one of these reinforced posts that was ran over almost with no resistance.

But perhaps the most terrifying attack wasn’t on Iranian soil. It involved Iranian citizens. On May 20, a pickup truck drove to an Iraqi army checkpoint in the city of Tal Afar. While waiting on line, the driver detonated the truck. 13 guards and civilians died, according to local press reports. The driver was an Iranian man in his mid-30s.

Abou Ebrahim Al Irani was in Iran, less than three months before the attack. ISIS had summoned him from the Talesh area in the Guilan province north of Tehran, to perform the unholy duty. Less than a week later, the head of Iranian Ministry of Intelligence’s branch in Guilan claimed that Iranian security forces have captured a Takfiri cell leader there. However, the security official, which Iranian state media didn’t name, didn’t say who was captured—whether Iran had really eliminated the cell which sent Abu Ebrahim to Iraq.

But if an Iranian extremist cell could so easily spare a suicidal jihadi to go to Iraq to perform an attack, the real question is: How many others are out there?

—with additional reporting by Noah Shachtman