Iran executed 29-year-old graduate student Erfan Shakourzadeh on espionage charges, accusing him of collaborating with the CIA and Israel’s Mossad during a period of heightened tensions with the United States and Israel.

Rights groups said the elite aerospace engineering student from Tehran’s Iran University of Science and Technology was tortured, held in solitary confinement, and forced to give false confessions before his execution.

In messages published before his death, Shakourzadeh denied the accusations as fabricated and urged the public not to remain silent about wrongful executions.

He was the fifth person executed on espionage charges since the conflict escalated in late February, as Iran has also increased executions tied to protests and opposition activity, CBS News has reported.

Human rights organizations accuse Iranian authorities of using executions and closed-door trials to intimidate society during periods of political unrest and international pressure.