Ukraine continues major incursion into Russia, with reports of advances amid heavy fighting

LONDON -- Ukraine has continued its major incursion into Russia’s Kursk region for a third day, with Russia still clearly not in control and Ukrainian troops appearing still to be moving deeper into Russia.

The attack appeared to be a large-scale offensive operation, involving at least two Ukrainian brigades, rather than a less significant cross-border raid. As scale of the attack was on Thursday becoming clearer, it appeared to be one of the most significant military developments in the war in months.

An Ukrainian adviser to the head of President Volodymyr Zelenskyy’s office, Mykhailo Podolyak, commented Thursday for the first time on the operation, saying one goal was to alter the Russian perception of the war, a shift that could potentially affect any eventual negotiations.

"This increases the cost of the war for Russia quantitatively. More armored vehicles have been destroyed, the Russian Federation has lost territories, and there have been more casualties. Will this affect how they perceive this war? Undoubtedly,” Podolyak said in a live discussion on Ukrainian TV.

The Ukrainian incursion began on Tuesday when a Ukrainian force numbering in at least the hundreds crossed over the border near the village of Sudzha, with tanks and heavy weapons, according to official and unofficial Russian public sources. Catching Russia off-guard, Ukrainian soldiers quickly seized a handful of villages, advancing up to 10 to 15 km, according to the pro-Kremlin Russian military bloggers.

Since then Ukraine has moved in significant reinforcements and its forces were continuing to try to press forward but were being held on Thursday at the village of Korenovo, according to multiple pro-Kremlin bloggers, who are close to Russia’s military. Heavy fighting was also focused on Sudzha, which Ukrainian troops were reported to have largely surrounded.

Russia’s defense ministry on Thursday claimed to have halted the Ukrainian advance and to have inflicted hundreds of casualties on Ukrainian troops. But reports from the Russian military bloggers suggested a far more chaotic situation, with unconfirmed reports Ukrainian forces had continued to reach deeper in some places into the Kursk region.

One of the best-known pro-Kremlin military bloggers, Two Majors, reported that six or seven Ukrainian tanks were fighting in the village of Ivnitsa, roughly 30 km from the border.

He also reported gunfire, likely from Ukrainian reconnaissance special forces units, in the village of Anastasevka, more than 30 km from the border and about 45 km from the Kursk nuclear power station.

Multiple military bloggers also reported gunfire, likely from Ukrainian reconnaissance special forces units, in the village of Anastasevka, more than 30 km from the border and about 45 km from the Kursk nuclear power station.

They also reported Ukraine engineering equipment to try and dig in and hold ground.

Ukrainian officials have been almost entirely silent on the operation, with speculation swirling around its possible goals. Ukraine may be seeking to pull Russian forces from elsewhere in Ukraine, as Ukrainian troops are under intense pressure in the Donbas region near the key city of Pokrovsk, although most analysts believe Russia likely has sufficient forces to continue its operations there unchanged.

Russian analysts have also suggested that Ukraine could be seeking to seize the Kursk Nuclear Power Plant, which is located roughly 80km from the border, but most analysts were deeply sceptical the Ukrainian force is large enough to reach it.

Podolyak’s comments on Thursday appeared to perhaps support another theory that Ukraine could be seeking to capture Russian territory with the goal of trading it for Ukrainian occupied land in potential future peace negotiations. Podolyak said he expects the Kursk attack to impact Russian society, bringing clear signals the ineffectiveness of Putin's strategy closer to home, at the same time as potentially strengthening Ukraine’s position in negotiations.

"Do they respond to anything other than fear?" he told Ukrainian television. "No, we need to finally realize this. Any compromise is perceived by Russia as your weakness and readiness to kneel before them. When can they sit at the negotiating table, and can something be achieved? Only if they understand that the war is not going according to their plan."

Some Ukrainian and independent military analysts have expressed doubts about the wisdom of such a risky operation when Ukraine is suffering from severe manpower shortages in Donbas, where Russia in recent weeks has been making rapid advances towards Pokrovsk, prompting fears Ukrainian lines near there are in danger of cracking. Russian forces overnight reportedly again made advances in that area, capturing another small village, according to Ukrainian military analysts.

ABC News' Natalia Popova contributed to this report.