An ammunition explosion caused by “careless” handling of a grenade in Russia’s Belgorod region on the border with Ukraine killed three people and injured 15, Russian news agencies reported on Sunday.

The blast occurred in a cultural centre repurposed for Russia’s armed forces to store ammunition, state news agencies reported, citing local emergency services for the toll.

Belgorod region borders Ukraine and is the location of several Russian military bases and training grounds.

Death toll in Russian missile attack on Dnipro apartment building rises to 21

The 112 and Baza Telegram channels, linked to Russia’s law enforcement agencies, said the dead and injured were conscripts called up to fight in Ukraine under a mobilization drive.

They reported that the blast occurred after a senior soldier mishandled a grenade in front of subordinates, accidentally detonating it. TASS said “careless handling of ammunition” caused the explosion.

Reports did not say when the incident took place.

Belgorod borders the northeast of Ukraine, just across from the city of Kharkiv, which has been targeted by multiple Russian missile attacks since the invasion of Ukraine last February.