An 11-year-old boy was burned alive after being "doused in petrol" and then locked inside a shed that erupted in flames.
Albert Umbetyarov, 11, was allegedly killed after a dispute with older children, say reports in Russia.
The young judo star was locked in a shed that was nailed shut before going up in flames in Dubovaya Roshcha, Moscow region.
The appalling incident comes amid reports of sharply rising crime among children during Vladimir Putin's war in Ukraine.
An eyewitness told Argumenti media outlet: "The attacking boys used bats to beat him to the almost unconscious state, then doused him with petrol, locked him in a shed, set the shed on fire and tried to escape."
Another said: "There was a fight. One of the younger children who witnessed it said that the victim was beaten at his knees, so he couldn’t run, or even walk."
The attackers were reportedly aged 13 to 15, and the horror was watched by girls who allegedly streamed the fire.
A third witness said: "They attacked him out of envy, because he was an athlete and was doing better than them.
"One of the boys from that group ran away and didn't take part.
"Younger children aged six and seven playing nearby then ran to adults to get help."
A father of the dead boy's friend said his son had left the scene before the horror and went back after eating his meal.
"At 7pm he called me in tears," said the father, Alexey.
"He told me: ‘My friend burned to death in the shed’. I went there.
"I saw the flames. There was no one to be rescued by that time."
Men had tried to use shovels to try and get through the inferno to the boy but failed, he said.
The boy's judo coach Alexander Tvanba said Albert was "smart and very peaceful", adding: "He wouldn't offend a fly. He was very hard-working and never had any issues. He won several competitions."
He believed the boy was unconscious when he was nailed inside the wooden shed.
Had he been conscious he would have been strong enough to smash his way out, he said.
The Russian Investigative Committee said: "On May 19, 2023 children during a quarrel shut a boy inside a shed, locked the shed from outside, and nailed the door.
"Next a fire started. According to preliminary findings, [the fire started] inside the shed.
"Children could not open the door, and asked for help. When help arrived, the boy's body was found inside the burned shed."
The committee's head Alexander Bastrykin said this month that a "general rise in crime is underway" in Russia.
"We see a trend when serious and particularly grave offences are being committed by children."
He also highlighted "an increasing tendency of extremist crimes committed by young people" with "sharp increase" in 2022 and 2023 "after the onset of the special military operation". Bastrykin was a university classmate of Putin's.
