Britain's defense ministry said Wednesday that a Ukrainian attack on a military barracks in a Russia-controlled city in eastern Ukraine may have been exacerbated by Russia storing ammunition close to where Russian troops were staying.

"Given the extent of the damage, there is a realistic possibility that ammunition was being stored near to troop accommodation, which detonated during the strike, creating secondary explosions," the ministry tweeted in its latest daily assessment.

The British defense ministry added that Russia had a history of unsafe ammunition storage before it launched its invasion of Ukraine, "but this incident highlights how unprofessional practices contribute to Russia's high casualty rate."

Russia's defense ministry said early Wednesday that its troops' "massive use" of mobile phones led to the January 1 strike.

"It is already obvious that the main reason for what happened was the switching on and massive use — contrary to the prohibition — by personnel of mobile phones in a reach zone of enemy weapons," the ministry said in a statement.

"This factor allowed the enemy to track and determine the coordinates of the soldiers' location for a missile strike," it added.

Ukraine claimed responsibility for the strike in Makiivka on Monday. Russian forces control the town and had turned a school into military quarters.

Russian Lieutenant General Sergei Sevryukov said in a video statement released by the ministry early Wednesday that the death toll had risen to 89, from 63 announced Monday. He said more bodies had been found under the rubble of the building, Agence France-Presse reported.

"A commission is working to investigate the circumstances of what has happened," he said.

Russian war correspondents said the soldiers in the Makiivka quarters consisted largely of newly mobilized Russians, according to AFP. They added the soldiers were stationed in an unprotected building that was destroyed because ammunition stored on the premises detonated in the strike.

On Tuesday, mourners gathered in several cities of the Volga region of Samara — where some of the servicemembers came from.

Ukrainian President Volodymyr Zelenskyy said in his nightly video address Tuesday that his country needs to strengthen its defenses. He has claimed for the past two days what he sees as Russia's plans for a new offensive.

"We have no doubt that the current masters of Russia will throw everything they have left and everyone they can muster to try to turn the tide of the war and at least postpone their defeat," he said. "We have to disrupt this Russian scenario. We are preparing for this." (KB/VOA)