On Saturday, gunmen killed 11 people at a Russian military training facility.
Two individuals opened fire on a group of volunteers who had enlisted to fight in Ukraine during a firearms training session, according to state-owned news agency Ria.
The attackers were from a former Soviet republic, the Russian defence ministry said, but did not give further details.
They were also shot dead during the incident in the Belgorod region of Russia, which borders Ukraine.
A further 15 people were wounded.
“During a firearms training session with individuals who voluntarily expressed a desire to participate in the special military operation [against Ukraine], the terrorists opened fire with small arms on the personnel of the unit,” Ria cited a defence ministry statement as saying.
“As a result of the shooting, 11 people were fatally wounded. Another 15 people with wounds of varying severity were taken to a medical facility,” it said.
The local governor said no residents of the Belgorod region had been killed or injured.
Last month Russian President Vladimir Putin ordered a mobilisation of 300,000 Russians who had previously done compulsory military service.
The order sparked protests across Russia and a surge of people attempting to leave the country.
Soon after the mobilisation was announced, a military recruiter was shot at an enlistment office in Siberia.
Last week, Putin announced that over 200,000 people had already been mobilized, and he saw no need for additional mobilization.