Russian President Vladimir Putin said moves taken by Wagner Group leader Yevgeny Prigozhin, a longtime ally, to bring his troops into a key Russian city amounted to a "stab in the back."

Putin didn't mention Prigozhin by name, but said that "necessary orders have been given" to defend Russia in a recorded address aired on Russian television on Saturday.

"Actions that divide our unity are in essence defeatism before one's own people," he said. "This is a stab in the back of our country and our people."

-ABC News' KJ Edelman

Russian President Vladimir Putin has been briefed by the country's security agencies about what was referred to as an "attempted armed rebellion," according to Russia's state-run media.

The late-night statement from Putin's spokesman suggested that the Kremlin considered Wagner Group's move into Rostov-on-Don, a key Russian city close to the border with Ukraine, to be a "rebellion."

Wagner's founder Yevgeny Prigozhin in an audio message on Friday claimed his forces would now punish Russia's defense minister and chief of general staff, telling other units to stand down and not offer resistance.

"Special services, law enforcement agencies, namely the Ministry of Defense, the FSB, the Ministry of Internal Affairs, Rosgvardiya, in round-the-clock mode, constantly report to the president on the measures taken in the context of the implementation of the instructions previously given to him," Kremlin spokesperson Dmitry Peskov said on Saturday.

-ABC News' Tanya Stukalova and Patrick Reevell

The Wagner Group is a private military organization run by Yevgeny Prigozhin, a longtime ally of Russian leader Vladimir Putin, with tens of thousands of fighters, according to U.S. officials.

Earlier this year, the U.S. labeled the group a "significant transnational criminal organization" and levied new sanctions, while human rights observers this week said they suspected Wagner fighters were linked to the mass killing of people in Mali last year.

Government reports, statements from U.S. officials and insights from experts, as well as other sources, shed light on the Wagner group's history and goals, its alleged wrongdoings and its importance to Russia -- in Ukraine and elsewhere in the world.

-ABC News’ Nathan Luna, Leah Vredenbregt and Ivan Pereira

Yevgeny Prigozhin, leader of the Wagner Group, said on Saturday that the headquarters of the Southern Military District and all military facilities in Rostov-on-Don were under his control.

Prigozhin in a video demanded that Kremlin bring him Chief of the General Staff Valery Gerasimov and Sergei Shoigu.

He also threatened in the video that he would go to Moscow.

"We will destroy anyone who stands in our way," he said in one of a series of video and audio recordings posted on social media.

He added, "We are moving forward and will go until the end."

The Kremlin on Wednesday acknowledged for the first time that a plane carrying Yevgeny Prigozhin, mercenary chief of the paramilitary Wagner Group, was possibly downed on purpose.

Kremlin spokesman Dmitry Peskov told reporters that investigators are looking into the possibility that the 62-year-old Prigozhin was assassinated.

"It is obvious that different versions are being considered, including the version -- you know what we are talking about -- let's say, a deliberate atrocity," Peskov said when asked about the investigation.

The plane carrying Prigozhin and nine others crashed in Russia's Tver region on Aug. 23, killing everyone aboard, according to the press service of Russia's Federal Air Transport Agency.

The crash came about a month after Prigozhin led a chaotic armed rebellion that threatened the longstanding leadership of Russian President Vladimir Putin.

On Friday, Peskov denied speculation that the Kremlin was involved in the plane crash, calling the allegation an "absolute lie."

The crash investigation is being conducted by the Russian Investigative Committee as a domestic incident and Peskov said that allowing in international investigators "is out of the question."

-ABC News' Will Gretsky