The destruction wreaked on a Russian battalion as it tried to cross a river in northeastern Ukraine last week is emerging as among the deadliest engagements of the war, with estimates based on publicly available evidence now suggesting that well over 400 Russian soldiers were killed or wounded.

And as the scale of what happened comes into sharper focus, the disaster appears to be breaking through the Kremlin’s tightly controlled information bubble.

Perhaps most striking, the Russian battlefield failure is resonating with a stable of pro-Russian war bloggers — some of whom are embedded with troops on the front line — who have reliably posted to the social network Telegram with claims of Russian success and Ukrainian cowardice.

“The commentary by these widely read milbloggers may fuel burgeoning doubts in Russia about Russia’s prospects in this war and the competence of Russia’s military leaders,” the Institute for the Study of War, a Washington-based research body, wrote over the weekend.

On May 11, the Russian command reportedly sent about 550 troops of the 74th Motorized Rifle Brigade of the 41st Combined Arms Army to cross the Donets River at Bilohorivka, in the eastern Luhansk region, in a bid to encircle Ukrainian forces near Rubizhne.

Satellite images reveal that Ukrainian artillery destroyed several Russian pontoon bridges and laid waste to a tight concentration of Russian troops and equipment around the river.

The Institute for the Study of War, citing analyses based on the publicly available imagery, indicated that there could have been as many as 485 Russian soldiers killed or wounded and more than 80 pieces of equipment destroyed.

As the news of the losses at the river crossing in Bilohorivka started to spread, some Russian bloggers did not appear to hold back in their criticism of what they said was incompetent leadership.

“I’ve been keeping quiet for a long time,” Yuri Podolyaka, a war blogger with 2.1 million followers on Telegram, said in a video posted on Friday, saying that he had avoided criticizing the Russian military until now.

“The last straw that overwhelmed my patience was the events around Bilohorivka, where due to stupidity — I emphasize, because of the stupidity of the Russian command — at least one battalion tactical group was burned, possibly two.”

Mr. Podolyaka ridiculed the Kremlin line that the war is going “according to plan.” He told his viewers in a five-minute video that, in fact, the Russian Army was short of functional unmanned drones, night-vision equipment and other kit “that is catastrophically lacking on the front.”

“Yes, I understand that it’s impossible for there to be no problems in war,” he said. “But when the same problems go on for three months, and nothing seems to be changing, then I personally and in fact millions of citizens of the Russian Federation start to have questions for these leaders of the military operation.”

Another popular blogger, who goes by Starshe Eddy on Telegram, wrote that the fact that commanders left so much of their force exposed amounted to “not idiocy, but direct sabotage.”

And a third, Vladlen Tatarski, posted that Russia’s eastern offensive was moving slowly not just because of a lack of surveillance drones but also “these generals” and their tactics.

“Until we get the last name of the military genius who laid down a B.T.G. by the river and he answers for it publicly, we won’t have had any military reforms,” Mr. Tatarski wrote.

Western military analysts have also pored over the imagery and say the attempted crossing demonstrated a stunning lack of tactical sense.

They have speculated that Russian commanders, desperate to make progress, rushed the operation. Some also suggested that it was a reflection of disorder in the Russian ranks.

If the estimates that hundreds of soldiers were killed or injured prove accurate, it would be one of the deadliest known engagements of the war.

There were more than 500 sailors aboard the Russian Black Sea flagship Moskva when it was struck by a Ukrainian missile in April. The Kremlin at first insisted that all the sailors were rescued, later saying one was killed. But even as the families of missing sailors have publicly demanded answers, the Kremlin has largely kept up an official silence on the fate of the crew, part of a larger campaign to suppress bad news.