WASHINGTON (Reuters) – Ukraine appears to be on track to achieve several of its key battlefield goals, a senior Pentagon official said on Monday, as Kyiv moves to bolster its military position against Russia before winter.

The optimistic assessment of Celeste Wallander, Assistant Secretary of Defense for International Security Affairs, came on the same day that Ukrainian forces made their biggest breakthrough in the south of the country since the war began.

Ukrainian forces burst across Russian lines and advanced rapidly along the Dnipro River, threatening the supply lines of thousands of Russian troops.

Wallander cited recent efforts in the southern Kherson region as recent successes in Kharkiv and Donetsk.

“Ukraine appears to be on track to achieve all three of these goals at the moment,” Wallander told the Center for Strategic and International Studies, a Washington think tank.

Russia’s setbacks drew harsh public criticism of the generals running the Russian war, and prompted Moscow to order a partial mobilization of forces.

However, a US military official told reporters at the Pentagon on condition of anonymity that Washington – which arms and advises the Ukrainian military – has not yet seen a large-scale Russian build-up of its forces in Ukraine.

“Overall, we’ve seen relatively small numbers (of Russian reinforcements) … but nothing on a large scale at this point in the game,” the official said.

Kyiv provided little information about its recent gains in the south, but Russian sources admitted that the Ukrainian tank attack had advanced tens of kilometers along the western bank of the river, recapturing a number of villages along the way.

“Ukraine’s goal is to block the Russian bridge on the western bank of the Dnipro River in Kherson,” Wallander explained.

She said that would be a “big defeat for Russia”.

“Because it hinders, more than that, Russia’s ambition to take over Odessa, which was one of the stated goals earlier this year,” Wallander said.

“It gets more difficult, and it gives Ukraine a much better defensive position to overcome what might be a lull in hot fighting during the winter.”

The advance in the south reflects the tactics that have brought Kyiv significant gains since the beginning of September in eastern Ukraine, as its forces quickly captured territory to control Russian supply lines, cutting off the larger Russian forces and forcing them to retreat.

On Friday, Ukraine regained control of Lyman, the main Russian stronghold in the north of Donetsk province. This opened the way for it to advance deep into the Luhansk Territory, threatening the main supply routes to the lands captured by Moscow in some of the bloodiest battles of June and July.

Wallander said Ukraine’s seizure of Lyman “would significantly affect Russia’s ability to supply, resupply and move forces along this front line of conflict.”

(Phil Stewart reports). Additional reporting by Tom Palmforth in Kyiv. Editing by Jonathan Otis

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