In a shocking turn of events, Yevgeny Prigozhin, the head of the Wagner mercenary group, has taken center stage as the leader of an armed rebellion, posing the greatest threat to Russian President Vladimir Putin's 24-year hold on power.

Former U.S. Ambassador to Russia John Sullivan, a CBS News contributor, told "CBS Mornings" that the turn of events surrounding the rebellion, which ended in a deal between Prigozhin and Putin, "doesn't speak well" about Putin's hold on power and the stability of the country.

"These extraordinary events not only give the appearance of weakness but actually show real weakness by Putin," Sullivan said. 

Prigozhin's revolt raises significant concerns about the control and future of Russia's massive nuclear weapons arsenal, impacting global security, according to Sullivan.

"It's really, I would think, the preeminent concern of American officials today: who's in control in Moscow and, in particular, who's controlling the largest stockpile of nuclear weapons in the world," Sullivan said. "That affects all Americans. It affects the entire world. And remember, we're talking about a country that is a permanent member of the U.N. Security Council. Russia is supposed to be helping to guarantee peace in the world. Instead, it's introduced war and chaos, and Putin controls a massive nuclear arsenal. So that's a grave concern."

Prigozhin's rise from a petty thief to a successful restaurant chain owner and his subsequent involvement in organized crime have been marked by intrigue and controversy.

Prigozhin gained recognition through his leadership of the Wagner Group, achieving territorial victories in Ukraine when the regular Russian military faced defeat, and they played a crucial role in the fierce battle of Bakhmut. 

Prigozhin said Saturday that he'd agreed to halt his forces' "movement inside Russia, and to take further steps to de-escalate tensions" in an agreement brokered by Belarusian leader Alexander Lukashenko.

As part of the deal, Wagner troops would be pardoned and criminal charges against Prigozhin would be dropped. 

Sullivan said that even this deal makes Putin seem weak. 

"Prigozhin was leading a military column to Moscow. And then Putin struck a deal with him and let him go free, that's extraordinary," Sullivan said.

In:
• Wagner Group
• yevgeny prigozhin
• Russia
• Vladimir Putin