Officials have not said what caused the October 22 blast in the city of Kopeysk, but have opened an investigation into industrial safety violations.

"The final list of victims of the tragedy includes 23 people," the regional government said on Telegram, up from a previous toll of 12 given the day after the incident.

Social media videos showed a fireball erupting into the night sky at the Plastmass plant, which produces explosives, including for the Russian army.

The explosion levelled one of the plant's buildings. Rescuers spent a week searching through the rubble for survivors and bodies.

Investigators pushed back against reports that it was caused by a Ukrainian drone attack.

Kopeysk lies in Russia's rust belt in the Ural mountains, home to many military enterprises, around 1,600 kilometres (1,000 miles) from the border with Ukraine.