A dual American-Iranian citizen was sentenced to 18 years in prison in Iran over the weekend on charges relating to espionage and “collaborating with a hostile government.” Reza “Robin” Shahini, 46, was visiting his mother in northeast Iran in July when he was arrested by Iranian Revolutionary Guard Corps while walking to a restaurant with friends.

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“It was a terrifying moment, and they blindfolded me and they took me to the custody and I did not know where I was,” Shahini said, speaking to VICE News via phone from prison. “They were interrogating me every morning, every afternoon, and I was always by myself in my cell.”

During his interrogation, he said, he asked to see the evidence against him. “They don’t answer such questions,” he said. “The thing is they are all brainwashed [to think] that the U.S. is a hostile government. Even the judge.”

He’s the latest in a string of dual nationals that have been arrested on questionable charges and dealt heavy prison sentences in the wake of the Iran nuclear deal. There have been at least five known cases of dual nationals from Canada, the U.K., and the U.S. detained by Iran since the deal was signed in January.

Hadi Ghaemi, executive director of the International Campaign for Human Rights in Iran, said he was “shocked” at the severity of Shahini’s sentence. “That is an unprecedented sentence for that charge,” he said. “It’s extremely harsh. It really demonstrates that the Iranian judiciary is out of bounds.”

The charge, he said, is supposed to be used for those accused of collaborating with countries with which Iran is at war. “The charge against him does not hold ground under Iranian law, because the United States is not a hostile government according to an opinion of the Iranian Supreme Court, because Iran is not at war with it,” Ghaemi said.

Shahini emigrated to the U.S. in 2000 at age 30 and has since completed an undergraduate degree at San Diego State University in international security and conflict resolution, and says he’s previously worked as a car salesman. He’d had planned to begin a graduate degree in homeland security at SDSU this fall.

Shahini did participate in the short-lived “Green Movement” of 2009, when thousands of Iranians took to the streets to protest what was seen as election rigging by former Iranian President Mahmoud Ahmadinejad, but supports the current president, Hassan Rouhani. The judge referred to Facebook posts that he had put up during that time as evidence.

In a statement to VICE News, the U.S. State Department emailed: “We have seen reports of the detention in Iran of Robin Shahini a person reported to be a U.S. citizen. The safety and security of U.S. citizens remains our top priority. We continue to use all the means at our disposal to advocate for U.S. citizens who need our assistance overseas.”

“As we’ve said before, the secretary raises the cases of detained and missing U.S. citizens anytime he meets with Iranian officials. Beyond that, we’re not going to get into the specifics of those conversations.”

Shahini told VICE News that he was planning to go on hunger strike to protest his imprisonment.

Since September 2015, Iranian authorities appear to have been targeting citizens they believe could upset the status quo, such as human rights activists, charity workers, or foreign journalists, like Washington Post reporter Jason Rezaian.

Other American-Iranian dual citizens who’ve recently been handed sentences for acting behalf of “enemy” governments include Siamak Namazi, a Dubai-based businessman, who received a 10-year prison sentence just last week, along with his 80-year old father.

The exact number of American dual-national prisoners is unknown, in large part because Iran and the U.S. have not had full diplomatic relations since the 1979 Iranian revolution and American embassy hostage crisis. The U.S. frequently uses the Swiss consulate in Tehran as a go-between to discuss sensitive matters.

Rezaian’s release this January — on the day the Iranian nuclear deal was signed — came as part of a broader prisoner swap between the U.S. and Iran. That swap has come under increased scrutiny in the last few months after it was revealed that the U.S. made a $400 million cash payment to the Iranian government during the same period.

Many critics of the Iran deal derided that payment as a ransom, although the U.S. State Department denied that charge, maintaining that the money was part of agreed upon reparations the U.S. owed the Islamic Republic based on international arbitration of assets seized during the Iranian revolution.

Earlier this Fall, at a Council on Foreign Relations conference, Iran’s foreign minister Javad Zarif denied having influence in the arrests, stating they fall under the domain of the Iranian judiciary, which is separate from the state government of president Hassan Rouhani.

The arrests come at a precarious time for the Iran nuclear deal. The agreement that was brokered by the Obama administration, but its future success may well be predicated on whoever occupies the Oval Office after the U.S. elections in November.

Officially, the nuclear deal was designed to block Iran’s path to making a nuclear weapon, by adding more IAEA checks and balances to Iran’s enrichment program, in return for an easing of economic sanctions. But many people living in the Iranian diaspora hoped that there will be an eventual thawing of relations between the two countries.

The arrests have prompted the U.S. State Department to issue one of its strongest travel advisory warnings on Iran in years.