Russia said on Wednesday that 89 soldiers died in the Ukrainian attack on Makiivka on Monday, raising the death toll from the originally stated 63. Ukraine has claimed a far higher casualty figure of around 400 fatalities.

Makiivka is twin city to the regional capital of Donetsk, controlled by Russian proxy forces since 2014.

According to the Russian defense ministry, four Ukrainian rockets hit a temporary Russian barracks in Professional Technical School No. 19, a vocational college, in the first minutes of the New Year.

The attack is a blow to Russian President Vladimir Putin, although most criticism in Russia has been aimed at military commanders.

Amid the fog of war, how much do we know about the attack, the deadliest single incident Moscow has acknowledged since the conflict began?   

What happened?

The strike hit the barracks at one minute past midnight on New Year's Day, Daniil Bezsonov, a Russian-installed Donetsk official, said.

Russia's defense ministry said six U.S.-made HIMARS rockets were fired by Ukraine.

Unconfirmed footage circulating on social media purportedly shows residents watching Putin's midnight address before running for cover as missiles strike the ground nearby.

News and social media footage shows buildings virtually razed as emergency service workers sift through rubble.

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What's been the official Russian response?

Russia's defense ministry on Wednesday blamed the unauthorized use of mobile phones by its troops as the main reason for the attack, rather than any military error or weakness.

"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." 

The governor of Russia's Samara region said many of the dead soldiers were locals.

What does Ukraine say?

Ukraine almost never publicly claims responsibility for attacks on Russian-held territory in Ukraine. But its General Staff confirmed the attack within hours, without specifying the suspected number of casualties.

Other Ukrainian defense sources later claimed around 400 people had died. Russian sources, including Igor Girkin, a former FSB officer instrumental in starting the initial 2014 Donbas conflict, said there were "many hundreds" killed and injured.

Ukrainian President Volodymyr Zelenskyy made no mention of the attack in his video address on Tuesday.

What's been the public reaction in Russia?

Criticism has been directed at military commanders rather than Putin, who has not commented publicly on the attack.

Russian critics have questioned why around 500 soldiers were reportedly being housed alongside an ammunition dump at the site, probably increasing the death toll.

Girkin blamed Russia's "untrainable" generals for the losses.

Reports that Ukrainian forces were able to identify the target from soldiers using their Russian mobile phones has provoked anger among Russia's military blogger community.

"As expected, the blame for what happened in Makiivka began to be blamed on the mobilized soldiers themselves. You see, they turned on their phones and got spotted," wrote Grey Zone, a Telegram channel linked to the Wagner Group mercenary outfit.

Grey Zone blamed commanders for lodging large numbers of soldiers in a building vulnerable to artillery fire.

In a post on Telegram, Sergei Mironov, leader of a Kremlin-loyal party in Russia's parliament, said that an investigation was necessary to determine whether "treachery or criminal negligence" was behind the strike. He said that officials responsible should be prosecuted.