Russia has blamed the illegal use of mobile phones by its own troops for a deadly Ukrainian missile strike – which reportedly resulted in the killing of at least 89 Russian soldiers.
The Ukrainian missile strike hit a temporary Russian barracks in a vocational college in Makiivka, in the occupied Donetsk area, on New Year's Day.
Moscow has reported the number of Russian soldiers killed in the attack had risen to 89, having previously said that 63 Russian soldiers were killed in the weekend strike with other, unconfirmed reports putting the death toll much higher.
Ukraine claimed that around 400 mobilised Russian soldiers were killed in the school building, with the Strategic Communications Directorate of Ukraine's Armed Forces adding that about 300 more were also wounded.
Neither figure has been confirmed.
Russian General Lieutenant Sergei Sevryukov said that phone signals allowed Kyiv's forces to "determine the co-ordinates of the location of military personnel" and launch a strike in the eastern Donetsk region.
He said measures were being taken to "prevent similar tragic incidents in the future" and promised to punish officials responsible for the failure.
The attack, one of the deadliest on the Kremlin's forces since the start of the war more than 10 months ago, happened one minute into the new year, according to Mr Sevryukov.
Ukrainian forces fired six rockets from a US-provided Himars multiple launch system at a building "in the area of Makiivka" where the soldiers were stationed.
Two rockets were downed but four hit the building and detonated, prompting the collapse of the structure.
Semyon Pegov, a Russian war correspondent has questioned the Russian ministry's reasoning.
In a Telegram post, Pegov said that Ukraine could have been able to locate the troops via drones and intelligence, not necessarily through mobile phones.
"The story of 'mobiles' is not very convincing," Pegov said. "I rarely say this – but this is the case when it would probably be better to remain silent, at least until the end of the investigation. As such, it looks like an outright attempt to smear the blame."
Ukrainian President Volodymyr Zelensky made no mention of the attack in a video address on Tuesday.
He did however highlight that Russia is preparing to step up its attacks on Ukraine using exploding drones.
"We have information that Russia is planning a prolonged attack by Shaheds (Iranian-made exploding drones)," President Zelensky said in his video address.
He added that the goal is to break Ukraine's resistance by "exhausting our people, (our) air defence, our energy", more than 10 months after the invasion.