At least 11 people were killed and 15 injured in a shooting Saturday at a military training base in the Belgorod region of Russia, which serves as a staging ground for the war in Ukraine, the Russian Defense Ministry reported.

The ministry said the victims were volunteers “who expressed a desire to participate in a special operation,” a Kremlin-preferred term for the war.

“Two citizens of one of the CIS countries committed a terrorist act at the training ground of the Western Military District in the Belgorod Region,” TASS state news agency reported, citing the ministry’s readout. CIS is the Commonwealth of Independent States, a union of Russia, Belarus, Moldova and several Central Asian countries.“The two terrorists were killed by return fire,” the statement read. It’s unclear whether the gunmen were among soldiers or had broken into the training ground.Baza, a Telegram channel with links to law enforcement, said the shooting happened Saturday morning at the military training ground in the Valuysky district, about nine miles from the Ukrainian border.The shooting comes amid a widely unpopular mobilization drive that Russian President Vladimir Putin announced three weeks ago in hopes of replenishing the ranks of depleted and exhausted units and turning around the stalling Russian war.

On Friday, Putin said 222,000 people have been called up, and 33,000 have been deployed to military units for subsequent combat missions. The Russian military said it is looking to recruit 300,000 new soldiers in total, though human rights groups have expressed concern that the actual number might be significantly higher.