State news agencies said Ali Akbar Siadat had confessed to receiving $60,000 for agreeing to pass on classified military information to Israel, including details of military flights and aircraft, manoeuvres and bases. Prosecutors said he received an additional $3,000-$7,000 for each separate transfer of intelligence.
The state agencies did not say if there was any direct connection with the execution of Ali Saremi, a veteran dissident who had been arrested four times since 1982 and, according to exiled opposition movements, had also been imprisoned under the regime of the late Shah.
The National Council of Resistance of Iran said he was a member of the People's Mojaheddin Organisation, the most prominent exile group, and had been last arrested three years ago for mounting a commemoration of the mass executions of dissidents in 1988.
The group is accused of being a terrorist organisation, though it says it has given up the violence it once espoused.
The motivation for Mr Saremi's execution may have been largely political, since the charges were that he conducted propaganda against the regime and was an "enemy of God". His death was ordered after a series of violent street confrontations in Tehran and other cities exactly a year ago on the day of Ashura, a Shia festival.
Both executions reflect the authorities' fear that opposition inside the country is growing and being strengthened by outside support.
Struan Stevenson, the British MEP who has taken up the Iranian exile cause in the European Parliament, said: "The mullahs subjected Mr Saremi to the most hideous and brutal torture in recent days in an attempt to break his spirit, but he remained steadfast and resolute to the end."
