Iran's Atomic Energy Organization said Sunday a hacking group broke into a subsidiary's network and had free access to its email system.

A statement issued Sunday described the content in the emails as “containing technical messages and routine and ongoing everyday exchanges.”

The comes after an anonymous hacking group calling itself Black Reward claimed responsibility for the breach and said it had released images of Iran’s nuclear facilities and at least 50 gigabytes of information from Iran's atomic energy organization.

Black Reward also published what it says are identity details and pay stubs of engineers and employees of the Iran Atomic Energy Production and Development Company, in addition to passports and visas of Iranian and Russian specialists working in the Bushehr power plant.

The group has demanded Tehran release political prisoners arrested in the recent nationwide protests.

The nationwide protests were sparked by the death of Mahsa Amini. She was arrested in mid-September by Iran’s morality police and died in their custody three days later. Amini, 22, was arrested for allegedly breaching the country's strict dress code for women.

Iran’s government has claimed Amini suffered a heart attack and was not mistreated. Her family said she had no history of heart trouble and that her body bore bruises and other signs of beating and mistreatment. (VOA)