Nine construction workers died after they were trapped in a blaze at a Russian mine on Sunday, according to Russian news agency TASS.
The Uralkali-operated potash facility is located in the Solikamsk district of the Perm Krai region, some 1,500 kilometres east of Moscow.
A fire broke out on Saturday morning, 340 metres underground. Eight workers managed to escape but nine others were trapped.
According to Uralkali representatives quoted by TASS, the fire spread through construction waste and foam.
Perm Krai's governor, Maxim Reshetnikov, later announced that a day of mourning would be held today (December 24).
President Vladimir Putin has ordered an investigation.
Euronews has contacted Uralkali for comment on the incident.