Russia’s operations in eastern Ukraine are narrowing in scope, the Pentagon assessed on Wednesday.
“Over the last days and even more than a week or so, you're starting to see Russian offensive operations become smaller in their size and scale,” the official said.
“You're seeing their objectives become more localised … it's just sort of a shrinking of their objectives, and their goals."
The official said towns, villages and sometimes only junctions were the targets. Russia is increasingly using company-sized units, they said.
A military company usually comprises between a few dozen and about 200 troops.
“This also goes to reinforce the notion that there just hasn't been much progress in the Donbas, [but] a lot of back and forth” between Russian and Ukrainian forces, the official said.
The Pentagon also assessed that a naval assault by the Russians was not on the horizon.
“There has been again no indication of an imminent naval assault here,” the official said.
The US has already rushed about $3.8 billion in military assistance to Ukraine since the February 24 invasion, with much more envisioned in a $40bn aid package working its way through Congress.
Western military aid including US anti-tank Javelin missiles have been crucial for the Ukrainian military.
The senior US official said 79 of the 90 howitzer cannon have been delivered and used in Ukraine, as well as more than 200 Switchblade and nearly 10 Phoenix Ghost drones.
The Pentagon’s latest assessment came as US Secretary of Defence Lloyd Austin met Swedish Defence Minister Peter Hultqvist.
Mr Austin said that Swede would greatly improve Nato if it joined.
“Your capabilities are modern, relevant and significant, and your addition to the alliance will make us all better at defending ourselves," he said.
"And of course, that’s especially important at this crucial time. The United States strongly supports Sweden’s application for Nato membership."
US President Joe Biden is meeting Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinisto at the White House on Thursday, to try to shore up support for their Nato membership.