Four people were killed on Tuesday by an explosion at a Russian gunpowder factory, state news agencies said, but an official was quick to rule out the possibility it was caused by an attack.
The blast happened at a plant in the Tambov region, about 400 km (250 miles) southeast of Moscow. Eight people were injured in the incident, the RIA news agency said.
Parts of south and western Russia are on high alert following a spate of attacks that Moscow blames on Ukraine, particularly on war-related targets such as fuel supplies and weapons stores.
Ukraine does not comment on military operations outside its borders.
Maxim Yegorov, Tambov's regional governor, said however that Tuesday's incident was caused by human error.
"The cause of the fire is the human factor. I can state unequivocally that this is not a terrorist attack. Unfortunately, there are human casualties. All necessary assistance will be provided to the victims," Yegorov said in a statement on the Telegram messaging app.
The fire had been put out and the plant was now working normally, he said.