Around 400 Russian soldiers were reportedly killed in a Ukrainian HIMARS missile attack in the occupied Donetsk region of Ukraine. The attack hit a building in the city of Makiivka, where Russian forces were believed to be stationed, just after the clock struck midnight on New Year’s Eve.

Pro-Russian authorities have acknowledged casualties, but have not confirmed the reported figures and claim that “far fewer” than 400 were killed. 

Russia’s Ministry of Defence later the same day claimed that 63 soldiers were killed, which still makes the death toll one of the highest for a missile strike in the war to date.

Daniil Bezsonov, a senior Russian-backed official in the occupied parts of Donetsk, said the missile struck Makiivka two minutes after midnight on New Year's Day, the BBC reports.

"A massive blow was dealt to the vocational school from American MLRS HIMARS," he said as cited by the BBC, referring to US-provided missiles. "There were dead and wounded, the exact number is still unknown," Bezsonov added in a post on Telegram.

The Ukrainian military claims that in addition to the estimated 400 killed, 300 were also wounded. The Ukrainian numbers have not been verified and experts warn they should be treated with caution, as both sides tend to over or underplay casualty figures.

Well-known pro-Russian commentator and a former leader of the Donbas rebels Igor Girkin seemed to confirm the Ukrainian reports, saying that “hundreds” had been killed and wounded, and the building where they were stationed had been “almost completely destroyed.” Despite his pro-Russian stance, Girkin has often criticised the Russian military leadership and their tactics.

HIMARS are high-precision missiles supplies as part of the US military support for Ukraine. In the previous week Ukraine used HIMARS to destroy a hotel in occupied Ukraine where several senior Russian commanders were believed to be staying.

If confirmed, then the strike has been the deadliest of the war so far.

The attack came the same day as Russia launched its own barrage against cities across Ukraine as the country prepared for the biggest holiday of the year. Rockets rained down on Kyiv and other cities across the country, but according to the latest information only one person was killed in Kyiv and 28 were injured, including a Japanese journalist, according to Ukrainian authorities.

The Ukrainian Defence ministry reported that 39 Iranian-made Shahed drones were eventually shot down by Ukraine during the attack. Energy facilities were also damaged in the attack, disrupting power and heating supplies, but the main body of missiles reportedly targeted residential buildings.

Russia has been targeting Ukraine's energy infrastructure for several months, causing destruction and power outages in the country throughout the winter months.