Russian businessman Yevgeny Prigozhin reacted sarcastically on Friday to new US sanctions against his Wagner private military group, and the Kremlin said Washington had been smearing Wagner without reason for years.
The United States on Thursday designated Wagner, which is fighting on the Russian side in some of the most intense battles of the Ukraine war, as a transnational criminal organization responsible for widespread human rights abuses.
In a statement via his press service, Prigozhin said: "We conducted an internal check on the subject of the Wagner group's crimes, but found nothing damaging. If anybody has any information about Wagner's crimes, please send it to our press service or publish it in the media, so we can help our American colleagues formulate their position."
Kremlin spokesman Dmitry Peskov said it was not the first time Washington had "demonized" the group.
"This has been going on for many years. As a rule, such statements from Washington are unfounded ... there is no evidence, no confirmation, nothing is presented to the public," he said.
After years spent operating in the shadows and denying his links to Wagner, Prigozhin acknowledged last September he had founded the organization, which has also dispatched soldiers to fight in Syria and in conflicts across Africa.
In recent months he has emerged as one of the key Russian figures in the war in Ukraine, clashing publicly with the defense ministry and army generals over Russia's faltering campaign strategy.
A former petty criminal turned confidant of President Vladimir Putin, Prigozhin has been recruiting convicts from Russian prisons to fight in Ukraine, promising them amnesty in exchange for a six-month stint at the frontline. Many have died in the war.
British defense chiefs said last week that up to 50,000 Russians could be fighting for Wagner in Ukraine alongside Russia's official armed forces.
Wagner personnel have been accused of multiple human rights abuses both in Africa and Ukraine.
In Mali and the Central African Republic, rights groups and witnesses say Wagner fighters were responsible for atrocities including rape, mass executions, torture, child abduction and physical abuse.
An ex-Wagner commander previously fighting in Ukraine who fled to Norway said earlier this month he saw Wagner soldiers being shot in the back as they tried to flee.