The family of a Swedish-Iranian researcher whose death sentence for espionage was upheld this week by Iranian authorities has dismissed the charges against him, saying his purported confession was "distorted" and that he was not in a position to gain access to the state secrets he is accused of divulging.

Ahmadreza Djalali, a permanent resident of Sweden who specializes in emergency medicine, was arrested in April while in Iran on business and later sentenced to death for spying for Israel.

Iranian authorities claim that Djalali delivered information on Iran's nuclear and defense plans and personnel to Israel's intelligence agency, Mossad, leading to the assassination of at least two nuclear scientists. The authorities also alleged that Djalali and his family received Swedish residency in exchange for cooperation with Mossad.

But after Tehran prosecutor Abbas Jafari Dolatabadi announced on December 25 that Djalali's death sentence had been upheld by the Supreme Court, the 46-year-old researcher's relatives decried the decision.

In an open letter to Iranian President Hassan Rohani, a copy of which was e-mailed to RFE/RL's Radio Farda, Djalali's mother, Najibeh Mortazavi, said that her son was innocent.

"Accusing someone like him, with his work and academic background who is committed to his country ... of ties to the Zionist regime and playing a role in the assassination of martyred nuclear [scientists] in exchange for money and residency in Sweden seems to be very unfair," Mortazavi, who resides in Iran, wrote in the December 26 letter.

Dolatabadi claimed that Djalali had provided Mossad agents with the names of senior employees of Iran's Nuclear Energy Organization. "The information delivered by [Djalali] includes complete data about 30 prominent members of Iran's military, defense, and nuclear projects, including martyrs Ali Mohammadi and [Majid] Shahriari," he said.

Mohammadi, a nuclear physicist, was assassinated in January 2010 while on his way to work. Shahriari, a nuclear engineer, was killed in November 2010 when a motorcyclist attached a bomb to his car. The assassinations came as Iran's nuclear research was under intense scrutiny, and amid accusations that Tehran was seeking to develop nuclear weapons.

State-controlled television broadcast a purported confession on December 17 in which Djalali admitted to supplying information to a foreign intelligence services about Iranian nuclear scientists who were later assassinated. But Djalali had previously denied the charges against him, and following the broadcast audio emerged in which he said he gave the confession under psychological pressure.

Djalali's mother wrote that her son "has rejected all the charges against him in court by providing credible documents. My son has never had access to the top establishment's secrets," she added.

Dolatabadi, who said he had met with Djalali in prison, claimed that the researcher had confessed to meeting eight times with agents of a "foreign spy agency" and receiving money, statements that concurred with his disputed televised confession.

But in a December 26 interview with RFE/RL's Radio Farda, Djalali's wife, Vida Mehrannia, said that the prosecutor had "distorted" her husband's comments.

"[Djalali] had said that these elements had corresponded with him eight times and that his response had been negative," said Mehrannia, who lives in Stockholm with the couple's two children.

She also said that the couple had received Swedish residency permit in order to study. "I've said it a number of times that we received a residency permit for study. All of the documents are available at Sweden's Migration Agency," Djalali's wife said.

Amnesty International said on December 12 that Djalali's lawyers had said that the court relied primarily on evidence obtained under duress and produced no evidence to substantiate the allegation that he was anything other than an academic peacefully pursuing his profession. The London-based rights group has called on Iran to quash Djalali's death sentence.

An online petition calling for the release of Djalali has gathered more than 270,000 signatures.

Iran is one of the world's most prolific practitioners of capital punishment, executing at least 567 people in 2016, according to Amnesty International. Most of the executions are carried out in relation to drug-related charges. International rights groups have condemned Djalali's arrest, saying it followed a pattern of Iran detaining dual nationals and expatriates without due process.

Written by Golnaz Esfandiari, with contributions by RFE/RL's Radio Farda broadcaster Farhang Ghavimi