Ukrainian military officials said “about 400” Russian troops killed

In one of their deadliest attacks yet on Russian forces, Ukrainians used American-made rockets to kill dozens — and perhaps hundreds — of Moscow’s troops in a New Year’s Day strike behind the lines, prompting outraged Russian war hawks to accuse their military of lethal incompetence.

The strike by the HIMARS rockets killed 63 Russian soldiers in a building housing them in the occupied city of Makiivka, in eastern Ukraine, the Russian Defense Ministry said on Monday — an unusual admission for a military that has often refused to acknowledge serious losses. A former Russian paramilitary commander in Ukraine, Igor Girkin, wrote on the Telegram app that “many hundreds” were dead and wounded and that many “remained under the rubble.”

Ukrainian military officials said it appeared that “about 400” Russian troops had been killed, though they did not explicitly say that Kyiv was behind the attack.

None of the claims could be independently verified, but even the lowest number would represent one of the worst Russian losses in a single episode in the war, and an embarrassment for President Vladimir V. Putin. He has vowed repeatedly to correct the glaring errors and weaknesses in his armed forces that the war has exposed, and in a New Year’s Eve speech filmed at a military base, Mr. Putin told the families of soldiers killed in the fighting, “I share your pain with all my heart.”

Pro-war Russian bloggers and some government officials said the debacle was caused by the military’s own repeated and costly mistakes, like garrisoning troops in a dense concentration within range of Ukrainian artillery, placing them in the same building as an ammunition depot, and allowing them to use cellphones, whose signals the Ukrainians can use to zero in on their target.

“Our generals are untrainable in principle,” wrote Mr. Girkin, who has used the nom de guerre Igor Strelkov.

Some pro-war lawmakers demanded an investigation, and one of them, Sergei Mironov, leader of a pro-Kremlin party in the Parliament, called for the prosecution of all officials responsible, “whether they wear epaulets or not.”

“Obviously neither intelligence nor counterintelligence or air defense worked properly,” he said.

The attack was “a massive blow,” said a spokesman for the Russian-installed proxy government in the Donetsk region, Daniil Bezsonov. “The enemy inflicted the most serious defeats in this war on us not because of their coolness and talent, but because of our mistakes,” he wrote in a Telegram post.

More than 10 months after an invasion that Russians — and many Ukrainians — thought would produce a quick Russian victory, each side has suffered more than 100,000 killed and wounded, by Western estimates, and the war has become one of attrition, with no evidence of an end in sight.

Some of the heaviest recent fighting has ravaged the Donetsk region, one of four the Kremlin claimed to annex in September even as its troops were losing ground there, giving up towns they had seized earlier in the war. Since then combat in the region has slowed to a bloody slog, as the Ukrainians look for places to press their advantage, while Russians build trenches and fortifications along the front lines and try to capture the city of Bakhmut.

On Monday, Russia launched a flurry of Iranian-made exploding drones at Ukraine, continuing its barrage against cities and civilian infrastructure, especially the power grid. But it appeared that Ukraine’s increasingly effective air defenses once again minimized the damage.

The Ukraine military said it had shot down all 45 Iranian Shahed drones launched over the weekend, though some cruise missiles penetrated its defenses.

The Ukrainian military said on Monday that 22 drones were shot down over Kyiv in the early-morning hours, but at least two loud explosions were heard in the city. Mayor Vitali Klitschko said some energy infrastructure facilities had been damaged, affecting systems that heat buildings. It was not clear if the explosions were caused by drones that evaded air defenses, by drones that were shot down but detonated on hitting the ground, or by air defense missiles.

In his nightly video address, President Volodomyr Zelensky warned on Monday, “We have information that Russia is planning a prolonged attack with Shaheds,” aiming to exhaust Ukraine’s defenses and its ability to endure. He said, “Now is the time when everyone involved in the protection of the sky should be especially attentive.”

The deadly attack on Russian forces in Makiivka used the HIMARS rocket artillery to hit a vocational school where troops were housed, Moscow said. The Russian Defense Ministry said that four HIMARS rockets had hit the building, and that two others had been shot down by Russian air defenses.

As pro-war bloggers and officials reacted with fury, video posted on social media showed firefighters amid the ruins of the structure, reduced to smoking piles of rubble. The bloggers have become influential opinion-makers in Russia amid the censorship of mainstream media.

Mr. Girkin, the blogger and former paramilitary commander, wrote that the vocational school in Makiivka had been “almost completely destroyed” because “ammunition stored in the same building” detonated in the strike. The ammunition was stored “without the slightest sign of disguise,” he wrote, adding that similar strikes had occurred earlier this year, albeit with fewer casualties.

Dara Massicot, a senior policy researcher at the RAND Corporation, noted that the Russian officials “do not typically provide this type of information after a major loss, which suggests they want to control the narrative on this event.”

Makiivka, adjacent to the city of Donetsk, lies only about 10 miles from the nearest Ukrainian-held territory, the town of Avdiivka to the northwest — well within the roughly 50-mile range of the HIMARS rockets the United States has sent to Ukraine. A U.S. military official declined to comment on the strike.

HIMARS, which fires satellite-guided rockets from mobile launchers, is part of a growing arsenal of sophisticated Western weapons that have helped Ukraine change the course of the conflict.

Last month, a Ukrainian HIMARS attack destroyed a hotel in the city of Kadiivka, in the Luhansk region northeast of Donetsk. That attack killed members of Kremlin-aligned Wagner paramilitary group who were using the hotel as a base, according to Ukrainian authorities in the region.

The HIMARS system is most effective when used against stationary targets that can be identified in advance and pinpointed, such as ammunition dumps, infrastructure or troop concentrations. The United States has so far supplied Ukraine with at least 20 HIMARS systems, which are made by Lockheed Martin.

Many soldiers who were casualties appeared to be new recruits, recently mobilized in Mr. Putin’s drive to conscript more men into the fighting in Ukraine. One report in Russian state media said that “active use of cellular phones by the newly arrived servicemen” had been a prime reason for the attack, helping Ukrainian forces to pinpoint their location.

Throughout the war, Russian soldiers in Ukraine have spoken on open cellphone lines, often revealing their positions and exposing the disarray in their ranks. Though the continued use of the phones, despite the devastating consequences, exposes a failing by the military command, military bloggers say this explanation shifts the blame onto the victims.

It does not address why Russian commanders housed so many conscripts in an unprotected building within reach of U.S.-made rockets.

“No one is assuming the responsibility for the needless deaths,” one blogger, Anastasia Kashevarova, wrote on Telegram.