MOSCOW

An explosion rocked a heating station in Russia's Tuva region in southern Siberia on Wednesday morning, injuring at least 21 people, six of them critically, and leaving three others missing, the Russian Emergency Ministry said.

The explosion caused a fire, and heavy smoke began to emit from a heating station in Shagonara, the ministry said in a statement.

"The explosion occurred in the station's boiler room, specifically at the fuel supply point with a belt container, and did not damage the boilers," it added.

Emergency services are currently engaged in extinguishing the fire and conducting a search and rescue operation, the ministry said.

Meanwhile, the Russian Investigative Committee has initiated a criminal investigation, citing charges of negligence that resulted in the incident and fire, which could have serious harmful consequences.