Ukraine's astonishing invasion of Russia is shown in online videos

The line of men dressed in camouflage clothing lying face down on the dirt road with their hands behind their backs is so long that the camera has to zoom out and pan to the left.

The video, which was widely shared on numerous official and unofficial social media accounts, is said to show more than 100 Russian soldiers being captured by Ukrainian forces in Kursk this week.

The date or circumstances under which the footage was shot could not be independently verified, but it is one of many that paints a picture of at least one side of Ukraine's stunning invasion of Russia.

The attack that turned the war on its head was made possible by surprise and secrecy – a surge in troops and equipment caught the Kremlin off guard. Its initial promises were shrouded in the fog of war and an information vacuum was left behind as official sources were very tight-lipped.

But as Ukrainian forces push deeper into Russian territory, the operation is being reinforced by a wave of images offering a glimpse into developments on the new battlefield: soldiers raising the Ukrainian flag over border villages, military vehicles rolling through Russian streets, and dozens of prisoners of war apparently captured.

Throughout the two-and-a-half-year war, a parallel conflict played out online, and this latest round offers a rare glimpse of what a surprise attack looks like on a modern battlefield.

All this was received by a weary Ukrainian public in need of a morale boost, as well as by a legion of observers straining to follow developments on the ground.

“The situation is very dynamic and there are many variables and changes, so the images and videos only reflect a certain part of the events,” said Emil Kastehelmi, a military analyst with the Finland-based Black Bird Group, which analyzes open source intelligence. “By geolocating images and videos and analyzing the material and the general situation in that direction, we can still say that Ukraine has the initiative and further gains are possible,” he told NBC News.

For the first five days after the August 6 operation, Ukraine did not even acknowledge that its troops were in Russia. In contrast, Moscow's Defense Ministry provided daily updates and released videos of its chaotic response to give the impression of being in control of the unraveling situation.

But then everything changed. Ukraine, apparently satisfied with the initial results, recognized the operation. And videos began to appear on social media, many of them filmed by invading soldiers, showing destruction and devastation in the Kursk region.

NBC News was able to geolocate a number of these videos, giving it a clearer picture of the Ukrainian incursion and its course.

A Russian border crossing near the key town of Sudzha, which Ukraine says it now fully controls, is seen after its destruction sometime between August 2 and 6, when the incursion began.

Then last Friday, a video emerged showing a convoy of burned-out military trucks next to a highway in the border village of Oktyabrskoye. Some of them bear the “Z,” the symbol of the Kremlin's war, and appear to contain corpses. The video drew the ire of influential Russian military bloggers, who asked why the trucks were traveling in a convoy under Ukrainian fire.

“The Russian government has done its best to hide the extent of its failure at Kursk from the Russian people, but modern communications technology, especially social media and the Internet, have made that impossible,” said Rajan Menon, director of the grand strategy program at Defense Priorities, a Washington-based think tank. “Not only is Putin unable to control events on the ground in Kursk, he also cannot control what Russians see and hear. The official narrative is categorically refuted by social media, photos and bloggers.”

Then the first evidence appeared on social media that Ukrainian soldiers were sighted in Russian border communities: the yellow-blue flag was raised in the settlement of Guevo in the southern part of Sudzha district; soldiers removed a Russian flag from an administrative building in the village of Sverdlikovo, right on the border.

One video showed a Ukrainian soldier posing cheerfully in front of a road sign northwest of Sudzha in the Kursk region, warning Russians that Ukrainians were approaching.

Another photo showed Ukrainian soldiers in military vehicles and on foot patrolling a residential street in a village in Kursk with weapons drawn.

Ukraine is apparently so confident of its control over Suzha that on Wednesday a Ukrainian television correspondent filmed troops tearing a Russian flag from a building in the city center. Foreign journalists followed shortly after.

And on Friday, several Ukrainian military social media accounts published for the first time clips of combat footage from the first hours of the invasion, accompanied by dramatic music.

“The use of social media images of Ukrainian forces in Russia actually appears to be an element of the overall Ukrainian strategy,” said Phillips O'Brien, professor of strategic studies at the University of St Andrews in Scotland. “They undermine Putin's reputation by showing Ukrainian troops on Russian soil – in good morale, well equipped and moving fairly freely in daylight.”

A flood of videos on social media, like the one showing the men lying face down in the dirt, purport to show Ukrainian soldiers taking Russian prisoners of war. Many of the videos were shared by Hochu Zhit (“I want to live” in Russian), a government group that Project of the Ukrainian military intelligence with the aim of persuading Russian soldiers to surrender.

The Russian Defense Ministry has released its own videos of Ukrainians allegedly captured in Kursk in recent days.

These images are important for Ukraine to refute the claim that they are facing an unstoppable force, O'Brien said. “The fact that large numbers of Russians are surrendering on Russian soil puts the Russian military in a very different light,” he added.