Two men gunned down a group of Russian soldiers on a military firing range in Belgorod on Saturday, killing 11 and wounding 15, Moscow authorities said.
The Defence Ministry said the two assailants from an unnamed nation in the Commonwealth of the Independent States, which groups nine ex-Soviet republics, were killed by return fire.
The ministry labelled the incident a "terrorist attack".
"During a firearms training session with individuals who voluntarily expressed a desire to participate in (the war), the terrorists opened fire with small arms on the personnel of the unit," RIA cited a defence ministry statement as saying.
Oleksiy Arestovych, an advisor to Ukrainian President Volodymyr Zelenskyy, 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 a majority of Russians living in western parts of the country, including Moscow, are Eastern Orthodox.
Some Russian independent media outlets reported that the number of casualties was higher than the official figures.
"A terrible event happened on our territory, on the territory of one of the military units," the governor of Belgorod region, Vyacheslav Gladkov, said early on Sunday.
"Many soldiers were killed and wounded ... There are no residents of the Belgorod region among the wounded and killed," Gladkov said in a video post on the Telegram messaging app.
Euronews was not able to independently verify the nationality of the two men or the Kremlin's casualty numbers.
The shooting comes amid a hasty partial mobilisation ordered by President Vladimir Putin to beef up Russian forces in Ukraine — a move that triggered
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