See inside the NYC-sized area of Russia that Ukraine seized in its lightning offensive

The Kremlin initially downplayed Kyiv's ongoing offensive, saying it was the work of a "sabotage and reconnaissance group."

But more than 100,000 Russian citizens have fled the region, and over 100 Russian soldiers surrendered or were captured since the lightning offensive began, a Ukrainian official said.

And Ukraine hasn't shown signs of backtracking in the face of reinforcements.

Earlier this week, Ukrainian President Volodomyr Zelenskyy said the defensive operation is meant to create a "buffer zone" to protect Ukraine, taking out key bridges to isolate Russian forces in Kursk.

As of Tuesday, Ukrainian forces have captured nearly 100 settlements in the Kursk region and control at least 1,263 square kilometers — roughly 488 square miles — of Russian territory since the shock invasion began.

By comparison, the area of New York City measures about 469 square miles, including both land and water, and the city of Los Angeles covers a total area of just over 500 square miles.

Plans for the Kursk offensive were largely kept under wraps, taking allied nations like the US and even some Ukrainian troops by surprise once the operation began.

Zelenskyy said the clandestine nature of the offensive was intentional, saying allies would have called the invasion "unrealistic."

On Tuesday, Ukrainian Commander-in-Chief Oleksandr Syrskyi said Ukrainian forces have captured more Russian territory in last two weeks than Russia has seized from Ukraine in all of 2024 so far.

The Ukrainian assault marks the largest attack by a foreign enemy on Russian soil since World War II. The Kursk region was the scene of one of history's largest battles where the Soviet Red Army turned the tide against the Nazis at huge cost, a conflict Russians remember as the Great Patriotic War.

On August 15, Zelenskyy announced that Ukrainian forces seized control of Sudzha, a key Russian administrative center located near a gas terminal that supplies gas from Russia to the rest of Europe via Ukraine. The capture could give Ukraine an opening to undermine Russia's economy by curtailing gas exports.

Sudzha covers nearly 1,000 square kilometers, or 385 square miles, making it the largest town in Russia that Kyiv has appeared to capture thus far.

While harrowing images of the Kursk region show the destructive aftermath during the incursion, Ukrainian officials said forces on the ground are making a point to provide aid and relief to Russian residents in the occupied territory, rather than dismantling infrastructure and targeting civilians, Russia has been accused of doing so in captured areas of Ukraine.

Ukrainian soldiers have given civilians water, canned goods, and other humanitarian aid, according to local reports. Ukrainian armed forces are also working in tandem with international humanitarian organizations to support the evacuation of civilians, according to a Ukrainian official.

As the Kremlin races to send reinforcements to Kursk in response to the surprise offensive, Russian President Vladimir Putin blamed the West for "waging war against us using Ukrainians," saying Kyiv has refused "proposals to return to the plan for peaceful settlement."

"But what kind of negotiations can we even talk about with people who indiscriminately strike civilians, civilian infrastructure or try to create threats to nuclear power facilities," Putin said in remarks last week. "What can we even talk about with them?"

Putin has demanded that Kyiv cede more land beyond what his troops have seized in over two years and abandon its NATO bid, with some hardliners going much further to demand that Ukraine surrender without conditions.

A US State Department spokesperson disputed claims that the US coordinated the assault with Ukrainian forces, saying "it's a little bit rich" for Russia to criticize Ukraine's ambitious offensive, given its own violation of "Ukraine's territorial integrity and sovereignty."

"Ultimately, the decisions about how Ukraine conducts its military operations are decisions that Ukraine makes," spokesperson Matthew Miller said. "Nothing has changed about our policy with respect to strikes across the border."

John Kirby, the US's national security communications advisor, had stronger words for the Russian president's complaints about the incursion: "There's an easy solution: He can just get the hell out of Ukraine and call it a day."