A total of 63 Russian soldiers were killed in a Ukrainian attack on a vocational school in Russian-occupied eastern Ukraine that took place in the early hours of New Year’s Day, the Russian Defense Ministry said Monday.

“As a result of the impact of four rockets with high explosive warheads on a center of temporary location, 63 Russian servicemen were killed,” the Defense Ministry said in a statement on Telegram.

Official Russian confirmation of the deadly strike came after details about the incident were widely publicized by Russian pro-war bloggers.

“There were a significant number of killed and wounded,” said Arkhangel Spetsnaz in a post on messaging app Telegram accompanied by a photo of still-smoking ruins.

“Yesterday evening they were still sorting through the rubble.”

Russian officials are traditionally tight-lipped about battlefield casualties and rarely acknowledge significant losses.

The Moscow-installed administration of Ukraine’s Donetsk region said Sunday that at least 25 rockets were fired by Ukrainian forces on New Year’s Eve as the fighting in the country intensified over a period that is a major holiday for both sides.

Russia launched several waves of missiles and drones at Ukrainian cities over the weekend, killing at least four people and wounding many others.

Most of those killed in the coal-mining center of Makiivka were reportedly Russians drafted as part of the country’s “partial” mobilization drive announced in September.

Russian military blogger Igor Girkin, a former intelligence officer critical of Russian military commanders, said on Telegram that the death toll could be even higher, possible as much as several hundred men.

The vocational college was “destroyed almost entirely as a result of the detonation of an ammunition dump in the same building. Almost all the military equipment, parked next to the building without any camouflage, was also destroyed,” Girkin said.

Similar posts about significant losses in Makiivka appeared on other Telegram channels, including those run by officials and pro-Kremlin journalists.

“One of the problems with relying on mobilized soldiers is that it is more difficult to disperse them because of a lack of small unit leadership, and they will do worse in the cold than trained soldiers,” tweeted military expoert Rob Lee.

“But housing them next to ammunition storage is simply a leadership failure.”

The Russian Defense Ministry said Ukraine used U.S.-supplied HIMARS missiles in the attack.

Ukraine identified the vocational school as a target because a high number of soldiers inside were using mobile phones, according to an unidentified Russian-appointed official quoted Monday by state news agency TASS.

The Ukrainian Armed Forces said Sunday that the death toll in the attack was about 400.