Russian authorities have launched a criminal investigation into terrorism over a blast at an explosives factory in central Russias Tambov region, the Kommersant business dailyreported Wednesday, citing unnamed sources.Police investigators have reportedly found fragments of a drone that attacked the Tambov gunpowder factory late Saturday, which caused a fire at the plant, though no one was killed or injured.The charges of terrorism, which Kommersant's sources say Russias Investigative Committee launched after the blast, carry a maximum prison sentence of 20 years.The Tambov branch of Russias Investigative Committee, which probes major crimes, hasnot commented on the attack.Kommersant reported that the Tambov plant, which manufactures artillery shells and gunpowder for small arms, was attacked for a second time early Tuesday.Russias militarysaidTuesday that air defense systems had shot down four drones in and around the Moscow region, including in Tambov, which is located some 400 kilometers south of the capital.In June, five people were killed when an explosion ripped through the Tambov gunpowder factory, withauthorities at the time blaming human error for the blast.A number of explosions have occurred at Russian arms factories in the 21 months since Moscow invaded Ukraine.