President Putin is going to make a TV address amid a dramatic challenge by the chief of the Wagner mercenary force.
Prigozhin called for a rebellion against the army – although he has denied attempting a coup.
On Friday night, security in Russia was tightened, the internet was restricted and military trucks were spotted on Moscow streets.
Early Saturday morning videos emerged purportedly showing Wagner forces entering the Russian city of Rostov-on-Don.
One video shows armed men in uniform surrounding the police HQ, while two tanks aim their guns at the building.
Residents of the city, near the Ukraine border, have been told to stay calm and remain indoors.
Prigozhin also accused the army of launching a deadly attack on his forces in Ukraine, where Wagner troops are fighting for Russia.
The Kremlin has ordered Prigozhin’s arrest, and he is being investigated for inciting mutiny.
Video appears to show Prigozhin meeting top Russian officials
A video which has emerged in the past few hours shows Yevgeny Prigozhin meeting with Russia’s Deputy Defence Minister Yunus-Bek Yevkurov.
It is unclear when the footage was taken, but it purports to show Prigozhin sitting down with Yevkurov and Vladimir Stepanovich Alekseev, the deputy chief of Russia’s military intelligence service.
Prigozhin has demanded a meeting with Russia’s chief of the general staff Valery Gerasimov and Russia’s Defence Minister, Sergei Shoigu.
The video was allegedly taken at Russia’s southern military headquarters in Rostov-on-Don.
The BBC has not independently verified the footage.
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