A gas blast on Wednesday night in the southern Russian region of Dagestan was caused by sabotage and a criminal case on charges of terrorism has been started, the Interfax news agency quoted the regional Interior Ministry as saying on Thursday.
The explosion set ablaze the main gas pipeline in Dagestan, which borders breakaway Chechnya, and two firefighters were injured and 19 bystanders sustained burns after the fire broke out at around 10:00 pm (1900 GMT) Wednesday, said Murtazali Gadzhiyev, Dagestan's regional emergency situations minister.
Investigators initially attributed the explosion to a technical failure, said the ministry, adding that another blast occurred about half an hour later.
Fire-fighters brought the fire under control at about 11:35 pm Moscow time (2035 GMT) on Wednesday. There were no civil houses nearby the site.
Wednesday's explosions left several districts of Dagestan and the neighboring nation of Azerbaijan without gas, NTV television reported. Repair work of the pipeline was under way and it is likely to restore supplies by Thursday night.
Chechen rebel leaders have threatened and been blamed for attacks on pipelines and other infrastructure in Russia.