The Wagner Group's Yevgeny Prigozhin responded to Russian President Vladimir Putin's calling him a "traitor," by saying he will not surrender or turn back.

"Putin was deeply mistaken about the betrayal. We are patriots of our homeland, we fought and are fighting," Prighozin said in an audio message. "No one is going to turn around at the request of the president, the FSB or anyone else, because we do not want the country to live longer in corruption, deception and bureaucracy."

Prigozhin accused Russia's military of targeting a Wagner column with helicopters and jets.

-ABC News' Patrick Reevell

The powerful head of Chechnya, the semi-independent Russian region, Ramzan Kadyrov, said on Saturday he supported President Vladimir Putin.

Kadyrov saiud he fully backs Putin and called Wagner Group leader Yevgeny Prigozhin's actions "treacherous."

Kadyrov has tens of thousands of heavily armed fighters. He said his forces are already moving to "zones of tension."

It raises prospect of Chechen forces fighting with Wagner Group troops.

Kadyrov has previously been friendly with Prigozhin -- his coming out in support of Putin is a boost for Putin, but also raises prospect of serious clashes in Russia.

-ABC News' Patrick Reevell

Russian leaders are "now choosing which side they are on," an advisor to Ukrainian President Volodymyr Zelenskyy said Saturday.

"The next 48 hours will define the new status of Russia," Mykhailo Podolyak said on Twitter. "Either a full-fledged Civil War, or a negotiated Transit of Power, or a temporary respite before the next phase of the downfall of the Putin regime."

He added, "A deafening 'elite' silence is in Russia so far..."

Members of the mercenary Wagner Group have begun moving north "almost certainly aiming to get to Moscow," in what amounts to the "most significant challenge to the Russian state in recent times," the U.K. Ministry of Defense said on Saturday.

"Over the coming hours, the loyalty of Russia's security forces, and especially the Russian National Guard, will be key to how the crisis plays out," the ministry said on Twitter.

Ukrainian troops have reportedly seized a small village on the Russian-occupied eastern bank of Dneipr after crossing the river from the liberated city of Kherson, according to Russian accounts on Tuesday.

A small Ukrainian force has managed to dig in to the village of Dachi after making a landing there a few days ago and are trying to expand the beachhead. Ukrainian troops in small boats crossed the river and landed at the base of the ruined Antonivskiy Bridge, which they destroyed last year.

Russian military bloggers reported very heavy fighting on Tuesday, saying Russian airborne units have been trying unsuccessfully to dislodge the Ukrainians for the past four days. Russian aviation and heavy artillery have been firing on the Ukrainian position.

So far, the Russian side claims some 70 Ukrainian soldiers are dug in, covered by intense artillery fire from across the river. The Russian accounts say Ukraine is trying to move reinforcements across. Video released by Ukraine also shows a Russian APC being destroyed in the village of Oleshkjy, further south, indicating the bank south of Kherson is now contested.

Ukrainian troops have also managed to advance and liberate Rivnopil, a village on the Zaporozhzhia front, breaking through after more than two weeks of fighting. It's notable because the Russians had been fighting hard to hold it.

Taken together the advance there, the landing in Kherson and advances near Bakhmut are small signs the Ukrainian counteroffensive may be starting to pick up steam and the Russians are coming under growing pressure.

-ABC News' Patrick Reevell