At least 11 people were killed and 15 more wounded at a Russian military training ground on Saturday when two attackers opened fire on a group of volunteers who wished to fight in Ukraine, RIA news agency said.
No civilians were killed in the attack at a military base in Russia's Belgorod region, but many soldiers were killed or wounded, the governor of Belgorod region Vyacheslav Gladkov said early on Sunday.
"A terrible event happened on our territory, on the territory of one of the military units," Gladkov said in a video post on the Telegram messaging app.
"Many soldiers were killed and wounded ... There are no residents of the Belgorod region among the wounded and killed."
The deadly incident is just the latest in a series of high-profile setbacks for Moscow's forces since the Feb. 24 invasion.
RIA, citing the defense ministry, said the two assailants had been shot dead after the attack in the southwestern Belgorod region, which borders Ukraine.
What happened at the Russian military training ground?
"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 defense 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.
Ukraine's response: The attackers were from Tajikistan
Oleksiy Arestovych, an adviser to President Volodymyr Zelenskiy, said in a YouTube interview that the attackers were from the Central Asian nation of Tajikistan and had opened fire on the others after an argument over religion.
Tajikistan is a predominantly Muslim nation, while around half of Russians follow various branches of the Christian church. The Russian defense ministry said the attackers were from a nation that belonged to the Commonwealth of Independent States, which groups nine ex-Soviet republics, including Tajikistan.
Reuters was not immediately able to confirm the comments by Arestovych, a prominent commentator on the war who appears in the media on an almost daily basis.
RIA did not say where the attack took place. The independent Russian news website Sota Vision said it had happened in the small town of Soloti, close to the Ukrainian border and about 105 km (65 miles) south east of Belgorod.
Authorities in Belgorod itself have repeatedly accused Ukraine of attacking targets in the city, including power lines and fuel and ammunition stores.
Ukraine has not claimed responsibility.