MOSCOW (AP) — Rescue teams on Sunday found the bodies of nine construction workers who were trapped inside a burning potash mine in Russia’s Ural Mountains, while Russian officials opened a criminal investigation of the accident.

A fire erupted Saturday at the mine operated by fertilizer company Uralkali in the Perm region east of Moscow. Uralkali said two teams of workers were doing maintenance work in the mine and operations had been suspended while they labored.

Officials said 17 construction workers were in when the fire broke out and eight of them were quickly evacuated. The blaze cut off access to nine other workers who were in a different section. Russian news agencies quoted the rescue operation’s headquarters as saying the rescue was refocused as an effort to recover the men’s bodies. Seven bodies had been removed from the mine by Sunday evening.