On Monday, a senior U.S. military official stated that Russia has largely surrendered its gains in Kharkiv and that the majority of its withdrawing troops have now crossed the border back into Russia.

The United States has received anecdotal accounts of Russian personnel abandoning their equipment, which "could be indicative of Russia's disorganized command and control," according to an anonymous U.S. military officer.

The statements to reporters at the Pentagon followed the weekend's quick advances by Ukrainian soldiers. The general staff of Ukraine has reported that its soldiers have reclaimed more than 20 towns and villages in just the previous day, as Ukrainian forces sweep deeper into territory captured from fleeing Russian troops.

In summarizing the Ukrainian achievements, the U.S. military official was optimistic yet cautious.

"It's obvious they're fighting hard," the official added, highlighting territorial gains in the south and east.

The general staff reported in an evening update that Ukraine withstood Russian assaults in two key regions of the Donetsk region: the city of Bakhmut and Maiorsk, near the coal-producing city of Horlivka.

However, according to a senior U.S. military officer, Russia continues to concentrate its gunfire on Bakhmut.

Under the condition of anonymity, the officer stated, "We continue to see heavy use of artillery and airstrikes."

Vitaly Ganchev, the Russian-installed head of Moscow's occupation administration in what was left of Russian-held territory in the Kharkiv region, admitted that Ukrainian forces had breached the border.

The official did not specify the number of Russian forces that had withdrawn from Ukrainian territory and returned to Russia but reported a considerable withdrawal.

"On the ground around Kharkiv, we estimate that Russian soldiers have largely abandoned their gains to the Ukrainians and have retreated to the north and east. The majority of these forces have crossed into Russia, according to the official.