LONDON (Reuters) - The Iranian foreign ministry said on Tuesday it had summoned the Swedish ambassador to protest over Sweden’s granting of citizenship to a Stockholm-based scientist being held in Tehran under a death sentence.

Ahmadreza Djalali, an Iranian academic with Swedish residency, was arrested in Tehran in April 2016 and later convicted of espionage, accused of providing information to Israel to help it assassinate Iranian nuclear scientists.

The prosecutor said Djalali had confessed to meeting agents of Israel’s Mossad intelligence agency to supply information on Iran’s nuclear and defense plans and personnel. Iran’s Supreme Court upheld the death sentence in December.

Iranian foreign ministry spokesman Bahram Qasemi was quoted as saying by state news agency IRNA that the Swedish envoy in Tehran had been summoned in protest on Monday.

“In the meeting, the Islamic Republic of Iran voiced strong protest against the action taken by the Swedish government to grant citizenship to an agent of Mossad who has confessed to participating in assassination of Iranian scientists,” Qasemi added.

The Swedish foreign ministry confirmed on Saturday that it had granted citizenship to Djalali.

“We have been in regular contact with Iranian representatives, requested access to Djalali and presented Sweden’s view of the death penalty, which we condemn in all its forms. Our demand is that the death penalty is not carried out,” a Swedish spokeswoman said.

Qasemi said Iran considered Sweden’s action “questionable and unfriendly”, and added that Tehran “could not accept the foreign nationality” of the detainee.

“He is still an Iranian,” he said.

Iran’s Revolutionary Guards have arrested at least 30 dual nationals since 2015, mostly on spying charges, Reuters reported in November.

Iran does not recognize the dual nationality of any detainees, a position that prevents Western embassy officials from visiting them.

Djalali had been on a business trip to Iran when he was arrested and sent to Evin prison. He was held in solitary confinement for three months and tortured, campaigning group Amnesty International has said.

Amnesty said Djalali wrote a letter from inside prison in August stating he was being held for refusing to spy for Iran.

Seventy-five Nobel prize laureates petitioned Iranian authorities last year to release Djalali so he could “continue his scholarly work for the benefit of mankind”.