Russia is executing soldiers who try to retreat from a bloody offensive in eastern Ukraine, the White House has said.
According to the US, some of the casualties suffered by Russia near Avdiivka were "on the orders of their own leaders".
Russian and Ukrainian troops have been locked into a fierce battle for the frontline town since mid-October.
Russia is thought to have suffered "significant" losses in this time.
Ukrainian estimates put the number of Russian casualties in Avdiivka at 5,000, while the US says that Russia lost "at least" 125 armoured vehicles and more than a battalion's worth of equipment.
A Ukrainian army spokesperson said that Russian troops were refusing to attack Ukrainian positions near Avdiivka because of heavy losses and that there had been mutinies in some units.
"Russia's mobilised forces remain under-trained, under-equipped and unprepared for combat, as was the case during their failed winter offensive last year," National Security Council spokesman John Kirby said in a briefing on Thursday.
He said that the Russian military "appears to be using what we would call 'human wave' tactics, just throwing masses of these poorly trained soldiers right into the fight."
"No proper equipment, no leadership, no resourcing, no support. It is unsurprising that Russian forces are suffering from poor morale," Mr Kirby added.
https://www.bbc.co.uk/news/world-europe-67234144