But Igor Girkin, a pro-Russian commentator, said hundreds had been killed and wounded, although the exact number was still unknown because of the large number still missing. The building itself was "almost completely destroyed", he said.
He added that the victims were mainly mobilised troops - that is, recent conscripts, rather than those who chose to fight. He also said ammunition was stored in the same building as the soldiers, making the damage worse.
"Almost all of the military equipment was also destroyed, which stood right next to the building without any disguise whatsoever," he wrote on Telegram.
Girkin is a well-known military blogger, who led Russian-backed separatists when they occupied of large parts of eastern Ukraine in 2014. He was recently found guilty of murder for his part in the shooting down of flight MH17.
Despite his pro-Russian stance, he regularly criticises the Russian military leadership and their tactics.