The US officials say that over 30,000 Wagner fighters have been killed since the commence of Russia-Ukraine conflict.
White House spokesman John Kirby said the group had suffered significant losses in recent weeks, with about 9,000 fighters killed in action.
Wagner has recruited lots of fighters in Russian prisons, and Mr Kirby added most casualties were untrained convicts.
Kirby added that despite the casualties, Wagner has made gains around the city of Bakhmut.
The US National Security Council spokesman questioned the military significance of the city.
Wagner fighters have announced that they had captured Paraskoviivka city in Ukraine.
Wagner started its activities in 2014 in Crimean Peninsula, and as Russia’s proxy in different areas, in particular Syria.
The Wagner Group is a Russian paramilitary organization that by recruiting volunteers takes parts in cinflicts.
The Wagner Group was much smaller before the war, with just 5,000 fighters, most of whom were experienced former soldiers, but after that it started recruiting new fighters.
Ukrainian President Volodymyr Zelensky has urged the West to “hurry up” in delivering weapons to Ukraine, as he warned that Vladimir Putin’s forces “can still destroy many lives”.