The Biden administration on Monday said it doesn't know Wagner Group chief Yevgeny Prigozhin's whereabouts, including which country he is in, following his short-lived rebellion against Russian President Vladimir Putin. 

State Department spokesman Matt Miller confirmed as much during a news briefing, adding that it was a "new thing to see President Putin's leadership directly challenged" amid Moscow's invasion of Ukraine. 

Prigozhin shocked the world this weekend when he turned his private military group against Russian forces, while taking control of Russian military bases. He relented on Saturday after Belarus held negotiations between the two sides.

The Kremlin said it made a deal in which the mercenary chief will move to Belarus and he and his soldiers will receive amnesty. 

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"I don't have any assessment about his location," Miller said of Prigozhin. "This certainly was a new moment."

On Monday, Prigozhin posted an 11-minute voice recording on social media outlining his reasons for going against Putin as his forces headed toward Moscow before an abrupt halt. 

The march toward Moscow was intended to be a protest against the prosecution of the war in Ukraine and not aimed at regime change in Russia, he said, according to a Reuters translation. 

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"We started our march due to injustice. We showed no aggression, but we were hit by missiles and helicopters. This was the trigger," the warlord said in the recording.

Prior to his revolt, Prigozhin had criticized Russian military leaders, including Defense Minister Sergei Shoigu and Chief of the General Staff Valery Gerasimov, for failing to provide his troops with enough ammunition during the bloody battle of Bakhmut. 

Miller said the conflict between Putin and his former ally is an internal Russian affair "in which the United States is not involved and will not the involved." He added that the U.S. does not take a position as to who leads Russia.

"We want a Russia that is not invading its neighbors and not trying to violate the territorial sovereignty of its neighbors," Miller said. 

He noted that Wagner forces have committed numerous human rights violations and generally bring destruction and chaos in any country the group operates in. 

Fox News' Anders Hagstrom contributed to his report.