"They are putting their priorities and their efforts in eastern Ukraine. And that's where still there remains a lot of heavy fighting," a senior defense official told reporters Friday. "We think they are trying to not only secure some sort of more substantial gains there as a potential negotiating tactic at the table, but also to cut off Ukrainian forces in the eastern part of the country."
Last week Russian President Vladimir Putin laid out a list of demands from Ukrainian President Volodymyr Zelenskyy in order to cease his military campaign in Ukraine.
The demands remain fairly ambiguous but disarmament, "de-nazifying," refrainment from joining NATO and protecting the Russian language were top priority items for the Kremlin.
Reports suggested that Putin may also seek to obtain territory in the Donbas region in eastern Ukraine – a demand Zelenskyy is expected to reject.
"They are fighting very hard in the Donbas area, and they have been for eight years – that's been a hot war and they have taken a lot of casualties," a senior defense official said. "I don't think anybody should just write off the Donbas as something that's not going to be significantly fought for by the Ukrainians."
The official said that Russian forces around Kyiv have stopped attempting ground advancements and have instead relied on air bombardment to attack the city.
"It's interesting that the bulk of their air activity is really only on Kyiv and Kharkiv, which remains a very bloody fight, and then the Donbas – that's where we're seeing the activity," the senior defense official said.
Security officials believe that Ukraine – which has been hit with more than 1,250 missiles since the war began four weeks ago – will continue to see air bombardment as Russian forces remain stalled on the ground.
Russian troops have been not only stalled throughout the country, but U.S. defense officials believe that Ukrainians are actually pushing Russian forces back near several key cities, including Kherson in the south and Kharkiv to the north.
"Clearly, they overestimated their ability to take Kyiv. And frankly, they overestimated their ability to take any population center, and they clearly underestimated the Ukrainian resistance," the official added.
Russia is believed to have maintained roughly 85 to 90% of its fighting force, which includes everything from soldiers to tanks, aircraft, artillery systems and naval power.
But the senior defense official noted that for the first time there are indications that Moscow is looking to send reinforcements into Ukraine by transferring troops from Georgia.
The number of troops to be moved remains unknown.
There is no indication that Russia is looking to bring in additional supplies or equipment at this time.