The death toll from an unexplained blast last week at a production facility in Russia's Ryazan region has jumped to at least 20 dead with another 134 people injured, local emergency services said on Monday, Reuters reported.

Pavel Malkov, governor of the Ryazan region that lies just southeast of Moscow, said on Friday that the incident had been triggered by a fire breaking out inside a workshop at the factory.

But it was unclear from Russian media reports what caused the fire or what exactly the factory was producing. Official Russian sources gave no details beyond efforts to find and treat the injured, according to Reuters.