Ukraine's incursion into Russian territory on August 6 surprised not only Moscow, but also many inside Ukraine itself and most of those who follow the war from the outside.
Why did Kiev decide to launch this bold attack when its troops are already thinned out in several places along the 1.000-kilometer front line?
Almost a week later, the Russian military is still having trouble stopping the incursion, but now the logic behind this operation is slowly beginning to emerge.
Here are five key questions about this new development in the war in Ukraine that will most likely affect how it plays out in the coming months.
- Ukrainian invasion of Russia: What will happen next
- Kyiv claims to be advancing in Russia's Kursk region
- Analysis: Ukraine's attack on Kursk shows that the war is not going according to Russia's plan
What happened in Kursk?
On August 6, Ukrainian troops made a surprise incursion into Russia's Kursk region, which borders Ukraine.
Reliable information about the scale of this attack is scarce.
At first it appeared as if the operation was on the level of earlier sporadic incursions by Russian saboteur groups opposed to the government of Vladimir Putin.
They were trying to cross into Russia from Ukraine and appeared to be made up of hundreds of ethnic Russians.
But last week's attack went deeper into Russian territory - when Russian military bloggers reported on fierce fighting going on thirty kilometers from the border and when the governor of the Kursk region told President Putin that 28 Russian villages had fallen into Ukrainian hands, it became clear that conventional Ukrainian troops participated.
It appears that while Moscow has been concentrating its military force on several key points on the main front line where fierce fighting continues, Kiev has decided to take advantage of the poorly guarded border and insert itself into Russia.
"We are on the offensive. The goal is to stretch the enemy's positions, to inflict maximum losses and to destabilize the situation in Russia since they are not capable of protecting their own border," he told the news agency. France Press an unnamed senior Ukrainian security official.
Why did Ukraine attack Russia in the Kursk region?
At first, Kyiv kept silent about this attack, and President Vladimir Zelensky indirectly confirmed it only on August 10.
He said that Ukraine continues to "push the war back to the aggressor's territory".
He did not give clear reasons or goals for this operation, but on August 12 he announced that Kiev now controls about 1.000 square kilometers of Russian territory.
Military and political analysts who have tried to answer the question "why" generally agree that one of the main reasons for this incursion could be a tactical distraction.
In recent months, Ukraine has struggled to contain Russian forces in the east, which have been slowly advancing, capturing the strategic Chasiv Yar last week.
In the north-east and south, the situation is equally difficult.
Despite the fact that Russia is outnumbered and outgunned at many points along the 1.100-kilometer front line, the Ukrainian authorities have decided to take a gamble by opening a new combat hotbed hundreds of kilometers away, in order to burden the enemy's manpower, diverting some of the pressure from eastern Ukraine to the Kursk region in Russia.
Security expert Mark Galeotti told the BBC that Ukraine had been locked in a war of attrition in recent months, with very little movement on the ground, and now had to take risks to gain any advantage.
"We sent our most combat-ready units to the weakest points on their border," said one Ukrainian commander, in a statement to Economist, confirming that it is a cube.
He added that the gamble did not begin to pay off as quickly as Kiev had hoped.
“Their commanders are not idiots… They are moving forces, but not as quickly as we would like. They know that we cannot expand logistics by 80 or 100 kilometers," he added.
How did Russia react?
Russian propaganda was quick to call the effort to suppress the Ukrainian incursion an "anti-terrorist operation".
Up to 121.000 people were told to evacuate from the Kursk region, and another 11.000 people were relocated from the neighboring Belgorod region.
Russian authorities have declared a federal state of emergency in the area, with individual financial compensation of $115 for local residents.
The Chief of the General Staff of the Russian Army, General Valery Gerasimov, claimed several times last week that the Ukrainian incursion had been stopped, while evidence to the contrary was visible on the ground.
General Gerasimov was conspicuously absent from the last session of the Russian Security Council, chaired by President Putin, dedicated to solving this crisis.
On the other hand, one of Putin's closest allies, head of the Russian FSB security service Alexander Bortnikov, was present.
In the latest statement about these events, President Putin accused Ukraine of attacking peaceful civilians and promised an "appropriate response".
Professor Galeoti says that Ukraine faces a real risk of fierce retaliation from Russia.
"Putin could announce a new wave of mobilization and bring several hundred thousand more soldiers into the armed forces."
He adds that Russia could find other ways to escalate the conflict.
In recent months, Ukraine has faced a devastating Russian bombing campaign of its energy infrastructure, leaving much of it destroyed or partially damaged.
This campaign could potentially become even more intense.
Does the fighting in the Kursk region mean that Ukraine has turned the tide of the war?
The ease with which Ukraine seemingly invaded Russia must be seen in a broader context and does not necessarily lead to an end to this conflict in the near future.
"It is an area of about 80 by 30 kilometers, and in the context of the size of Russia and Ukraine, it is negligible. But its political influence is much more important," says Mark Galeotti.
Some analysts claim that Ukraine is eager to show its Western allies, especially the United States, that its forces can continue to fight.
It also strengthened, if only temporarily, Kiev's negotiating position: with troops 30 kilometers inside Russian territory, Moscow seems unlikely to accept any proposal to freeze the battle lines as they currently stand.
The operation also changed the narrative of the war for Russians inside the country - no longer some distant conflict called a "special military operation", but a development that affects them all directly.
"When you look at the coverage of the Kursk region, even within the highly controlled environment of the Russian media, it's clear that some are starting to ask questions," says Sarah Rensford, the BBC's Eastern Europe correspondent.
How will the invasion affect the future of Zelenski and Putin?
For both the Russian and Ukrainian leaders, this is a turning point in their presidential mandates.
For Vladimir Putin, an authoritarian and often inflexible leader, accustomed to relying on his inner circle and the security services in particular, this development represents a great challenge.
It is becoming increasingly difficult to hide the extent of Russian military losses.
With tens of thousands of displaced Russians, it is difficult to maintain the image that the Kremlin is in control and that this is not an all-out war.
As Mark Galeota says, "every time it adds more and more cogs to the wheels of the Kremlin's propaganda machine."
"We've seen in past wars, from the Soviet war in Afghanistan to the Russian wars in Chechnya, that the Kremlin manages to maintain a certain narrative, and then, after a while, the real world begins to emerge more and more."
For Vladimir Zelensky, this incursion into Russia could turn out to be just as unpleasant, but for completely different reasons.
Analyst Emil Kastehelmi says the best outcome for Ukraine would be for Russia to divert "a significant amount of manpower from the most critical places to regain every square kilometer of Russian territory, despite losses."
Although it could boost Ukrainian morale in the short term, it could result in even greater territorial losses in the east, in front-line areas where fighting continues unabated, while some Russian military bloggers celebrate new breakthroughs, which for now yet they remain unconfirmed.
Professor Galeotti says the current stalemate in the war needed a shake-up to get things moving.
And while that shake-up is well underway, its outcome is uncertain for now.
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