Two days before a fire ripped through a section of Iran's Evin prison and killed at least eight people, a riot police unit arrived at the compound and began to patrol the corridors, shouting "God is Greatest" and banging batons on cell doors, six sources have said.

The patrols at the Tehran jail began without any apparent provocation by inmates, the sources said. These patrols continued from Thursday to Saturday, when some prisoners reacted by shouting for the downfall of Supreme Leader Ayatollah Ali Khamenei, echoing protests raging across Iran since September.

"Then we heard shots and chants of 'Death to Khamenei' by prisoners in other wards," said an inmate inside ward 8, which holds mostly prisoners convicted of financial crimes.