The scenes were decidedly Russian. A Gazprom facility. Flags with the country’s signature three horizontal stripes of white, blue and red. A Pyatyorochka supermarket.

The soldiers posting the videos, verified by The New York Times, were Ukrainian, almost giddily showing off just how easily they had pushed over the border and through Russian lines of defense in the past week.

In the Russian town of Sverdlikovo, a Ukrainian soldier climbed onto another’s shoulders, broke off the wooden post anchored to a town council building and threw the Russian flag to the ground. In Daryino, a town five miles to the west, other soldiers also grabbed a Russian flag. “Just throw it away,” a Ukrainian soldier said, grinning, as another flexed his muscles.

On Aug. 6, Ukraine launched an audacious military offensive, planned and executed in secrecy, with the aim of upending the dynamics of a war it has appeared to be losing, town by town, as Russian troops have ground forward in the east. The operation surprised even Kyiv’s closest allies, including the United States, and has pushed the limits of how Western military equipment would be permitted to be used inside Russian territory.

For Russia, it was a moment nearly as shocking as the mercenary Yevgeny V. Prigozhin’s march on Moscow in June 2023: the vaunted security state that President Vladimir V. Putin had built crumbled in the face of the surprise attack, failing in its basic task of protecting its citizens. And the unwritten social contract that has largely accompanied Mr. Putin’s 30-month campaign — that most Russians could get on with their normal lives even as he waged war — was cast into question anew.