Mr Ahmady said he was held in solitary confinement in Evin Prison north of Tehran for three months after his arrest in 2019 and blindfolded on repeated interrogations. The detention was so excruciating that he longed to be interrogated, as it was the only form of human contact he received.

“You will only be mentally retarded and insensitive to your surroundings,” Ahmady told the British broadcaster Channel 4.

Mr. Ahmady, who is of Kurdish descent, was born in northwestern Iran and obtained British citizenship in the 1990s. He has published several reports and books on genital cuts and child marriage in Iran. In a report published in 2015, he wrote that genital cutting was “embedded in the social fabric of Iranian culture” in at least four provinces.

“I know for a fact that my sentence is a tool for the Iranian security services and the Ministry of Justice to intimidate and pressure the few remaining people who work on social issues,” Ahmady said in the statement released on Wednesday its website was published.

According to local reports in December, Tehran prosecutors accused him of collaborating with the United States and others, which he denied.

More than half a dozen foreigners and dual nationals are held in Iranian prisons, including Ms. Zaghari-Ratcliffe; Fariba Adelkhah, a Franco-Iranian academic; Siamak Namazi, a businessman, and his father, Baquer Namazi, a former Unicef ​​official, both Iranian-American; Dr. Ahmad Reza Jalali, a Swedish-Iranian doctor and researcher; Nahid Taghavi, a German-Iranian architect; and Morad Tahbaz, an Iranian-American environmentalist.

Kylie Moore-Gilbert, a British-Australian scholar arrested in 2018 for spying for Israel, was released in December in a prisoner swap with three Iranian men.

Farnaz Fassihi contributed to the coverage.