Hours after Aleksei Agafonov arrived in the Luhansk region on 1 November as part of a battalion of new conscripts, his unit were handed shovels and ordered to dig trenches throughout the night.

Their digging, which they took turns to do because of the lack of available shovels, was abruptly interrupted in the early hours of the next day as Ukrainian artillery lit up the sky and shells started raining down on Agafonov and his unit.

“A Ukrainian drone first flew over us, and after that their artillery started to pound us for hours and hours, nonstop,” Agafonov, who survived the shelling, told the Guardian in a phone interview on Monday.

“I saw men being ripped apart in front of me, most of our unit is gone, destroyed. It was hell,” he said, adding that his unit’s commanders abandoned them just before the shelling started.

Agafonov was called up on 16 October alongside 570 other conscripts in Voronezh, a city in the south-west of Russia, as part of Vladimir Putin’s nationwide mobilisation push that has seen more than 300,000 men drafted to go and fight in a war that the Kremlin calls its “special military operation”.

After the attacks stopped, Agafonov, with roughly a dozen other soldiers, retreated from the forest outside the Luhansk town of Makiivka to the nearby Russian-controlled city of Svatove. In Svatove, Agafonov and his group moved into a deserted building, trying to contact other mobilised soldiers who had been with him that night.

According to Agafonov’s estimates, only 130 draftees out of the 570 survived the Ukrainian attack, which would make it the deadliest known incident involving conscripts since the start of the mobilisation drive at the end of September.

“And many who survived are losing their minds after what happened. No one wants to go back,” Agafonov said.

The incident points to Russia’s willingness to throw hundreds of ill-prepared conscripts on to the frontline in Ukraine’s east, where some of the heaviest fighting has been taking place, in an effort to stem Kyiv’s advances.

There is growing anger in Russia as more coffins return from Ukraine, bringing home the remains of conscripts.

Some of the details surrounding last week’s shelling could not be independently verified. But the Guardian spoke to a second soldier, as well as two family members of surviving soldiers, who gave similar accounts.

“We were completely exposed, we had no idea what to do. Hundreds of us died,” said the second soldier, who asked to remain anonymous. “Two weeks of training doesn’t prepare you for this,” he said, referring to the limited military training conscripts received prior to being sent to Ukraine.

The Russian investigative outlet Verstka, which first reported on the incident on Saturday, cited the account of a third soldier, Nikolai Voronin, who similarly described coming under Ukrainian fire in the early hours of 2 November.

“There were lots of dead, they were lying everywhere … Their arms and legs were torn off,” Voronin told Verstka. “The shovels we used to dig our trenches were now being used to dig out the dead.”

The shelling has led to anguish in Voronezh, where a group of wives of the mobilised men recorded an angry video message on Saturday addressing the local governor.

“On the very first day, they put the draftees on the frontline. The command left the battlefield and fled,” Inna Voronina, the wife of a drafted soldier whose fate is unknown, said in the video.

The mother of another soldier can be heard saying: “They tell us over the phone that our sons are alive and healthy and even fulfilling their military duty. How the hell are they alive and healthy when they were all killed there?”

Last Friday, Putin boasted that Russia had mobilised 318,000 people into its armed forces, citing a high number of “volunteers”. He went on to invoke the popular Russian saying “we don’t leave our own behind”, claiming the phrase was “not empty words”.

But the chaotic mobilisation campaign, and the casualties that have followed since, have drawn criticism among even the most enthusiastic supporters of the war.

In a scathing statement on Telegram, Anastasia Kashevarova, a well-connected pro-war journalist, condemned Russian commanders on the ground who she said were mobilising untrained men.

“Groups of [mobilised men] are abandoned without communication, without the necessary weapons, without medicines, without the support of artillery,” she said. “Zinc coffins are already coming. You told us that there would be training, that they would not be sent to the frontline in a week. Did you lie again?”

In one video, purportedly filmed at a training centre in Kazan, the capital of Russia’s Tatarstan region, dozens of recently mobilised men are seen berating its military leadership over a lack of pay, water and food. An officer identified as Maj Gen Kirill Kulakov is seen retreating as the large crowd of enraged conscripts shout insults at him.

Perhaps sensing the growing discontent, Putin said on Monday that he planned to “personally discuss with Russians” the issues surrounding support for the mobilised. He urged local officials to “pay attention” to mobilised soldiers and their needs.

Despite the seemingly high costs, the mobilisation drive has so far not resulted in Russia gaining new ground, according to a recent report from the Institute for the Study of War, a Washington-based thinktank.

The report said the Russian army was “wasting the fresh supply of mobilised personnel on marginal gains” instead of massing sufficient soldiers to ensure success.

“Russian forces would likely have had more success in such offensive operations if they had waited until enough mobilised personnel had arrived to amass a force large enough to overcome Ukrainian defences,” the institute said last Thursday.

In another sign indicating poor morale and communications at the front, several pro-Kremlin journalists published an open letter reportedly from an elite Russian naval infantry unit that criticised its superiors’ decision-making after huge losses in what it called an “incomprehensible” assault on the village of Pavlivka.

Russian forces launched an offensive on Pavlivka, south-west of Donetsk, on 2 November, according to the Ukrainian military and pro-Russia officials. Four days later, the 155th Guards Naval Infantry Brigade reportedly accused its military leaders of the loss of 300 men in a letter to Oleg Kozhemyako, the governor of their home region in the far-east of Russia.

“We were thrown into an incomprehensible offensive,” the letter was quoted as saying by a number of prominent pro-war bloggers.

While the Guardian was not able to independently verify the contents of the letter, Kozhemyako appeared to acknowledge that it was genuine but said it overstated the true scale of the losses.

“We contacted the commanders. Yes, there are losses, there’s heavy fighting, but they are far from what is written in this appeal,” he said in a video statement on his Telegram channel. “I am sure that in any case the situation will be analysed and the competent authorities will give their assessment.”