Chechen leader Ramzan Kadyrov said Russia was "finding it difficult" in the Ukraine invasion.
Russian propaganda sought to portray the invasion as a triumph, but Russia has encountered setbacks.
Kadyrov's forces have played a key role in Ukraine, including a failed plot to assassinate Volodymyr Zelenskyy.
Chechen leader Ramzan Kadyrov, a key ally of Russian President Vladimir Putin, admitted that Russia is encountering "difficulties" in its invasion of Ukraine.
At an event in Moscow, Kadyrov addressed the Russia's faltering invasion of Ukraine, in which Kadyrov's militias have played an important role and suffered heavy casualties.
In the televised remarks, Kadyrov insulted German Chancellor Olaf Scholz, whose government has provided weapons and diplomatic support to Ukraine. Kadyrov called Scholz "schizophrenic," according to a tweet by BCC Monitoring's Francis Scarr.
He went on to lament the difficulties faced by Russia in the invasion.
"And today we're fighting not against Ukraine, against Banderites [a reference to a pro-Nazi Ukrainian leader in the 1940s], we're fighting against NATO. NATO and the West, their mercenaries are there. And that's why our state is finding it difficult," he said.
"But it's a really good experience and we'll prove once again that Russia cannot be defeated."
Kadyrov, leader of the Chechen Republic, has been among the most aggressive Kremlin allies in the conflict, urging Russia to ditch peace talks with Ukraine, claiming to have fought on the front line, and challenging Elon Musk to a fight on Twitter over backing he has given Ukraine.
According to Ukrainian officials, Kadyrov and Chechen fighters were involved in a plot to assassinate Ukrainian President Volodymyr Zelensky in the early days of the conflict.
Since then Russia has abandoned plans to seize Ukrainian capital Kyiv in the face of significant losses, and concentrated on a more limited mission in eastern Ukraine.
Russian propaganda has shifted in the face of defeats and setbacks. In Putin's Victory Day speech on May 9 he sought to portray the conflict as being a struggle not just against Ukraine but vast NATO forces. A former Russian military officer was openly critical of Russia's campaign in live TV remarks this week.
The new tone was echoed in Kadyrov's remarks Tuesday.