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.
The workers were trapped 364 meters (1,200 feet) underground, and it took several attempts before searchers could safely reach the site. Firefighters were unable to extinguish the blaze for more than 36 hours.
The Perm region declared Monday a day of mourning for the workers who died at the mine in Solikamsk, which is located 1,200 kilometers (740 miles) east of Moscow.
Russian President Vladimir Putin urged regional authorities and investigators to conduct a thorough probe into what happened inside the mine.
Authorities were treating the incident as a result of lax safety procedures. The Investigative Committee said Sunday it launched a criminal probe of possible safety violations and had detained four employees of the subcontractor which was in charge of the maintenance work.
Poor safety standards are often to blame for recurring accidents in Russian mines. The last major Russian mining accident took place in August 2017, when 17 people died after a diamond mine in Siberia flooded.