Video purportedly shows Russian groups fighting Kremlin 3:09

(CNN) -- An apparent attack on Russian soil by anti-Putin Russians, who were fighting in support of Ukraine, sparked confusion and anger in Moscow.

Residents of settlements attacked in Russia's Belgorod region have been resettled to other areas as authorities continue to "clear territory" following the cross-border incursion launched from Ukraine, officials said Tuesday.

One civilian was killed as a result of the fighting, according to the regional governor, Vyacheslav Gladkov.

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However, questions remain about those responsible for the attack, how it took place and what implications it has for the war.

Here's what you need to know.

What happened in Belgorod?

The two groups of Russian citizens opposed to Putin, who fight in Ukraine as part of the Kyiv defense forces, the Freedom Legion for Russia and the Russian Volunteer Corps, claimed responsibility for the attack in the Belgorod region of southwestern Russia, which borders northeastern Ukraine.

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"Residential and administrative buildings and civilian infrastructure were subjected to mortar and artillery fire. As a result of these criminal actions, several civilians were injured," Russia's investigative commission said on Telegram in announcing an investigation into the attack.

Then two areas of the region were attacked overnight by unmanned aerial vehicles (drones), Gladkov said, causing two houses to catch fire.

A helicopter flies over Russia's Belgorod region, the scene of fighting between Russian defectors and pro-Kremlin troops amid the war in Ukraine. Credit: astrapress/Telegram

It appears to be the first time since Russia invaded Ukraine that Kyiv-aligned forces have launched a cross-border ground operation against Russian targets.

Aleksey Baranovsky, a representative of the Kyiv-based Political Center of Russia's Armed Opposition — the political wing of the Freedom Legion for Russia — told CNN that the operation had begun Sunday night and that fighting was "continuing."

He did not specify the number of fighters who had crossed the border into Russia. Baranovsky said the group wanted to "liberate our homeland from Putin's tyranny."

At first, Gladkov said no one had been killed, but later on Tuesday he said: "Unfortunately, we have losses. A civilian from the village of Kozinka was killed by the Ukrainian Armed Forces."

Russia's Defense Ministry said at a daily briefing Tuesday that its forces repelled the attackers back into Ukrainian territory through airstrikes, artillery fire and military units. He also added: "Those who remained of the nationalists were expelled to the territory of Ukraine, where they continued to be hit by fire until they were completely eliminated."

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What groups are involved?

The Freedom for Russia Legion said on Telegram early Tuesday that it and another group, the Russian Volunteer Corps, "continue to liberate the Belgorod region." The publication described the groups as "patriotic volunteers" and claimed that Russia was vulnerable to attacks, as "Russia has no reserves to respond to military crises. All military personnel are killed, wounded or in Ukraine."

As one of his fighters, who wears the "Caesar" badge, says in a video statement he recorded with his comrades before joining a cross-border raid on his homeland: "Russia will be free."

CNN's Sam Kiley interviewed that same fighter in December as the group fought for Ukraine against Russian attacks on the frontline town of Bakhmut.

"From the first day of the war, my heart, the heart of a true Russian, a true Christian, told me that I had to be here to defend the people of Ukraine," Caesar said. CNN agreed not to reveal his name to protect his identity.

"It was a very difficult process," Cesar said of joining the Ukraine effort. "It took me several months to finally join the ranks of Ukraine's defenders."

Now with his family in Ukraine, where he believes they are safer, Caesar said he was one of about 200 Russian citizens currently fighting alongside Ukrainian troops against their own country's armies. CNN has not been able to independently confirm this number.

How is the incident in Russia interpreted?

When Russian authorities condemned the attack, analysts noted widespread confusion in the Russian news space about how the attack was allowed to take place and how Moscow should respond.

Russian bloggers and pundits reacted with "a degree of panic, factionalism and incoherence, as often happens when they suffer major news shocks," the Institute for the Study of War (ISW) think tank wrote in its daily briefing on the conflict.

"The attack took Russian commentators by surprise," the ISW assessed.

This has the potential to prove embarrassing for President Vladimir Putin, who for 15 months has been leading an invasion that he baselessly claimed was necessary to keep Russia safe. With limited performance on the battlefield, Putin may now face discontent that the war is disrupting life at home.

Earlier this month, the Kremlin published an incident in which two drones flew over the Kremlin. It is still unclear who was responsible — Moscow blamed Ukraine for what it called an attack on Putin's life; Ukraine and the United States denied any involvement — but Putin's domestic critics could frame the dramatic video as a visual example of Moscow's war crumbling.

A still image shows a flying object exploding in an intense burst of light near the dome of the Kremlin Senate building earlier this month. Credit: Ostorozhno Novosti/Reuters

In another incident Monday night, the Freedom Legion for Russia posted a video on Telegram that appears to show the so-called blue and white flag of Free Russia flying over Moscow State University.

Other videos released by the group also appear to show another Russian opposition flag flying over several areas of the Russian capital.

The group did not claim direct responsibility for the incidents and CNN was unable to independently verify the reports.

What does Kyiv say?

As has often happened in the wake of alleged violence on Russian soil since Moscow invaded Ukraine, the incident has sparked very different narratives between the Kremlin and Kyiv.

Kremlin spokesman Dmitry Peskov on Tuesday described the instigators as "Ukrainian militants from Ukraine," even though the group claiming responsibility is made up of Russian citizens. Peskov had earlier said Kremlin forces were working to oust a "sabotage and reconnaissance group," according to state media TASS.

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A Ukrainian official acknowledged that the units had carried out an operation in the area, but insisted they were acting independently.

"We can confirm that this operation was carried out by Russian citizens," Andriy Yusov, a representative of Ukraine's defense intelligence agency, told CNN.

Yusov said the units were "part of the defense and security forces" when they were in Ukraine, but were independent of Kyiv when they were not: "In Russia they act as independent entities."

What will this mean for the war?

The attacks are unlikely to spark a change of momentum in the wider war in Ukraine, which has largely focused on Ukraine's eastern regions and seen few territories change hands for several months. The conflict is virtually at a stalemate and is more likely to be affected by Ukraine's spring counteroffensive against Russian forces, which may already be underway.

However, like previous hotbeds of tension away from the front lines, it has the potential to shape the narrative surrounding the conflict in both Russia and Ukraine.

Moscow has always been keen to present an image of Russian victimhood as a pretext for escalating attacks on Ukraine, given its public claim that the invasion is an act of self-defense and is necessary to keep Russia safe. Putin will no doubt try to use these attacks to reinforce that narrative, even though Kyiv denies it had any official involvement.

A short-term display of anger may also occur. After previous incidents that have embarrassed Russia — such as the murky drone incident over the Kremlin this month and the attack on the bridge connecting Russia to occupied Crimea in October — Moscow responded with a barrage of missile attacks across Ukraine, including the capital, Kyiv.

Putin is likely to want to focus Russia's attention on incidents occurring off the front, where his forces are striving to deal a heavy blow to Ukrainian defenses, as evidenced by costly and lengthy multi-month efforts to capture the relatively insignificant town of Bakhmut.

-- CNN's Victoria Butenko, Anna Chernova, Sam Kiley, Vasco Cotovio, Peter Rudden and Olha Konovalova contributed to this report.

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