Black snow has fallen in the Siberian city of Omsk for the second time in a week, a news report said Friday.
Omsk residents first noticed the black snow on Wednesday but were assured that the snow did not present any health risks, RIA-Novosti reported Friday.
Residents have now turned to the Federal Inspection Service for Natural Resources Use with a request to look into the snow's abnormal color, the report said.
With full tests to get the bottom of the freakish weather expected to take a few days, local prosecutors announced Friday that they were running checks into two Omsk-based businesses, coal producer Omsktekhuglerod and Thermal Power Station No. 5, to determine whether they could be at fault.
It's not the first time that Omsk residents have been exposed to unusual climatic conditions. In the summer, residents raised the alarm after they witnessed white powder falling from the air.
The powder turned out to be an oxidizing agent used at a nearby Gazpromneft refinery. The refinery was fined but has denied its guilt.