Moscow's indiscriminate attacks have devastated several Ukrainian cities since it sent tens of thousands of troops into its eastern European neighbor on February 24, with the civilian toll soaring and more than ten million people fleeing their homes.

Many analysts still see no clear path out of the conflict.

Even so, Ukraine's resistance -- backed by millions in Western military aid -- has been unexpectedly fierce, and now the Ukrainians are "in places and at times going on an offensive," Pentagon spokesman John Kirby told CNN.

"They are going after Russians and pushing them out of places where the Russians have been in the past," he said, particularly in Mykolaiv, in the south. "We have seen this now increase over the last few days."

Kirby said he could not confirm reports from Ukrainian officials that they had retaken at least one town and expect to take more in coming days.

But it would be "consistent with the kind of fighting and the kinds of capabilities we have seen the Ukrainians use," he said.

As for the Russians, he echoed Western analysts who have said the invading forces have become bogged down.

"They are running out of fuel. They're running out of food. They are not integrating their operations in a joint manner the way you would think a modern military would," Kirby said.

He cited communication problems between air and ground forces, and how in some cases the Russians have had to resort to using cellphones.

The Russians are "frustrated" and "stalled," he said, citing the fact the Russians have failed to take control of population centers beyond two areas around Kherson and Melitopol in the south.

"They are slowed. And some of that ... is due to their own ineptitude."