By Kathleen Magramo, Christian Edwards, Aditi Sangal, Adrienne Vogt, Leinz Vales, Tori B. Powell and Amir Vera, CNN
From CNN's Josh Pennington and Jennifer Hauser
Kyiv Mayor Vitali Klitschko said there were explosions early Saturday in Kyiv's central Solomyanskyi district.
"In Solomyanskyi district, fragments of a rocket hit the upper floors of a 16-story building. There is smoke on the upper floors. One victim was treated at the scene, another was hospitalized. There is no fire in the building. Rescue services are working at the scene," Klitschko wrote on Telegram.
The Kyiv City Military Administration said on Telegram that air sirens had been sounded.
From CNN's Kevin Liptak
US officials determined as early as January that there was an internal power struggle underway between the mercenary Wagner Group and the Russian government, and have been gathering and closely monitoring intelligence on the volatile dynamic ever since.
As Russia’s invasion of Ukraine stalled earlier this year, top American officials said they saw indications of tension between the Kremlin and the Wagner chief Yevgeny Prigozhin. They said they believed those tensions would mount over the coming months.
Officials said their assessments of the situation derived from intelligence, an indication of how seriously the White House and Pentagon took the potential for a power struggle to cause further instability in the ongoing conflict.
In January, a top White House official said Wagner was becoming a “rival power center to the Russian military and other Russian militaries.”
Officials suggested at the time that Prigozhin was working to advance his own interests in Ukraine instead of the broader Russian objectives.
The Wagner Group, which the West claimed had recruited prison convicts for fighting in Ukraine, was making decisions based on “what they will generate for Prigozhin, in terms of positive publicity,” John Kirby, the National Security Council spokesman, said in January.
Since then, White House and other US national security aides have been highly attuned to what one official said was an “ongoing battle” between Prigozhin and the Russian defense ministry.
From CNN staff
Yevgeny Prigozhin, the bombastic chief of Russia’s private mercenary group Wagner, appears to be falling out of favor fast in Moscow, after he unleashed a tirade against the Russian military on Friday and vowed to retaliate against its leaders.
Russia’s domestic intelligence service, the FSB, has opened a criminal case against Prigozhin, accusing him of “calling for an armed rebellion.” It also urged his own mercenaries to detain him.
Here’s what you need to know:
What did he do? Prigozhin on Friday accused Russia’s military of attacking a Wagner camp and killing a “huge amount” of his men. He vowed to retaliate with force, insinuating that his forces would “destroy” any resistance, including roadblocks and aircraft.
Prigozhin later rowed back on his threat, saying his criticism of the Russian military leadership was a “march of justice” and not a coup – but by that point he appears to have already crossed a line with the Kremlin.
Late on Friday, Prigozhin said his fighters had entered Russia’s Rostov region.
What Russia's saying. Russia’s defense ministry has denied attacking Wagner troops, calling the claim “informational propaganda.” And the FSB also opened a criminal case against Prigozhin for his threats, accusing him of calling for “an armed rebellion.”
Russian President Vladimir Putin is aware of the situation, according to Kremlin spokesman Dmitry Peskov.
Russian officials meanwhile appeared to take no chances with security measures stepping up in Moscow, according to Russian state media TASS. Social media posts showed military vehicles were seen driving around the main streets of the Russian capital in the early hours of Saturday.
From CNN's Mariya Knight
Yevgeny Prigozhin, the chief of the private military group Wagner, accused the Russian military's chief of staff Valery Gerasimov of ordering an aerial attack “in the middle of civilian cars.”
“The Chief of the General Staff has just given the order to raise the planes and open fire on the columns that are moving among civilian vehicles and trucks,” Prigozhin said. “He doesn't care who he kills. They have been killing their civilians for a year and a half instead of fighting the enemy.”
Prigozhin praised the Russian pilots for “refusing to carry out these criminal orders."
CNN cannot confirm Prigozhin's account of an aerial attack. He had earlier said his forces had entered the Russian Rostov region, which borders Ukraine.
The Russian defense ministry has not yet commented.
From CNN's Katharina Krebs
Russian Prosecutor General Igor Krasnov made a report to President Vladimir Putin about initiating a criminal case against Wagner Group chief Yevgeny Prigozhin, according to Kremlin spokesperson Dmitry Peskov.
"The Prosecutor General of the Russian Federation Krasnov reported to Putin about initiating a criminal case in connection with an attempt to organize an armed rebellion," he told Russian state media RIA Novosti in a comment on Friday.
According to him, the Prosecutor General also informed the president on the legality of initiating such a criminal case.
From CNN's Mariya Knight
Yevgeny Prigozhin, the chief of the private military group Wagner, said his fighters are entering the Russian Rostov region, which neighbors Ukraine.
“Now we are entering Rostov. The units of the Ministry of Defense, or rather the conscripts, who were thrown to block our road, stepped aside,” Prigozhin said, adding that at the moment his units “have crossed the state border in all places."
"The border guards came out to meet and hugged our fighters,” he said.
Prigozhin also accused Russian Defense Minister Sergei Shoigu and Chief of the General Staff Valery Gerasimov of “making a decision to destroy the disobedient units (of Wagner PMC) that are ready to protect their Motherland.”
Prigozhin warned against anyone obstructing him: "We will destroy everything that gets in our way," he said.
The Wagner chief's statement comes as Russian state media TASS reported a stepped-up police presence in Rostov late Friday.
CNN cannot independently verify these claims.
From CNN’s Uliana Pavlova
The Russian Ministry of Defense said early Saturday that Kyiv is concentrating several brigades for an offensive in the Bakhmut direction, taking advantage of Wagner Group chief Yevgeny Prigozhin's “provocation.”
"Taking advantage of Prigozhin's provocation to disrupt the situation, the Kyiv regime is concentrating units of the 35th Marine Brigade and the 36th Mechanised Brigade of the AFU (Armed Forces of Ukraine) in Bakhmut tactical direction at the initial line for offensive actions,” the defense ministry said in a statement.
Russia says its forces are fighting back.
“The servicemen of the Yug Group of Forces are defeating the enemy with air and artillery strikes," it said.
From CNN's Mariya Knight
Security measures have been stepped up in Moscow on Friday following explosive comments from Wagner private military leader Yevgeny Prigozhin, according to Russian state media TASS.
"Security measures have been strengthened in Moscow, all the most important facilities, state authorities and transport infrastructure facilities have been taken under increased protection," Russia's law enforcement agencies told TASS.
According to law enforcement, the Special Purpose Police Unit and Special Rapid Response Unit of the Russian Guard were raised on alarm as well, TASS reported.
Russia's FSB said it was investigating Prigozhin for "armed rebellion" after he vowed retaliation after accusing the Russian military of bombing his mercenary camp.
From CNN's Mariya Knight, Yulia Kesaieva, Katharina Krebs and Darya Tarasova
Sergey Surovikin, Russia’s top commander in Ukraine, urged Wagner mercenary fighters on Friday evening to "stop" and to "obey the will" of President Vladimir Putin.
"I’m addressing the leadership, commanders and fighters of Wagner. Together with you, we have traveled a difficult and hard path. We fought together, took risks, suffered losses and we won together. We are of the same blood. We are warriors. I urge you to stop, the enemy is only waiting for the internal political situation to worsen in our country," Surovikin is seen saying in a video posted to Telegram by a Russian state media reporter.
"You can’t play into the hands of the enemy in this difficult time for the country. While it is not too late, please obey the will and the orders of the Russian Federation’s president that was elected by the masses," Surovikin said. "Stop the columns, bring them back to the points of permanent dislocation and communication areas... Solve all the problems peacefully under the leadership of the Commander in Chief of Russian Federation."
Lt. Gen. Vladimir Alekseev, a Russian intelligence official, also posted a video criticizing Wagner's actions on Friday, saying "This is a coup d'etat."
“What is happening now is a blatant fact of insanity. I cannot explain it in other words," Alekseev said in the video.
"Our country is in the most difficult position right now," he continued. "When the whole Western world is turned against us. When the shells are coming from the whole world. Such things, that you started to fulfill now under someone's provocation idea will lead to enormous losses. First of all, enormous political losses. Imagine the enthusiasm that this will be taken with by the West."
"Only the president has the right to appoint the top leadership of the armed forces, and you are trying to encroach on his authority. This is a coup d'etat. There is no need to do this now, because there is no greater damage to the image of Russia and to its armed forces," Alekseev said.