Kherson, the southern Ukrainian city that was the first major population centre captured at the start of the war, is "contested territory again," a US defence official has told journalists.
If the city, which is relatively close to the Crimean peninsula, were to be retaken by Ukraine, it would represent a major setback for Russia's offensive.
Russia's military has disputed that it has lost control of Kherson, and Ukrainians on the ground there have not reported that it has been recaptured.
"The Ukrainians are trying to take Kherson back, and we would argue that Kherson is actually contested territory again," the Pentagon official told reporters on Friday.
"We can't corroborate exactly who is in control of Kherson but the point is, it doesn't appear to be as solidly in Russian control as it was before," added the official, who was speaking on condition of anonymity.
Fighting is ongoing in the larger region of Kherson Oblast, according to the latest reports, as Russia continues to focus its efforts on taking the southern Black Sea coast.