Russian forces appear to be "several days behind where they wanted to be" in their latest assault on Ukraine's Donbas region, a senior U.S. defense official said on Friday.

Driving the news: Russian troops pulled back from Kyiv and refocused their efforts on the Donbas region earlier this month after failing to seize the Ukrainian capital. The Pentagon believes Russian forces intended to be further along in their efforts to completely encircle Ukrainian troops in the east, the official said.

• Moscow's forces have not been able to link its units in the north with those in the south.
• "In fact, they're nowhere close to linking north with south as the Ukrainians continue to fight back," the official said.

What they're saying: Russian forces are using artillery and some airstrikes before moving in their ground forces, but these ground movements are making "plodding, uneven progress," the official said.

• "The artillery and airstrikes that they're launching against Ukrainian positions are not having the effect that they want them to have," the official said. "The Ukrainians are still able to resist ... So that's why we think this progress has been slow and uneven still over the last 24 hours."
• "We also assess that because of this slow and uneven progress — again without perfect knowledge of every aspect of the Russian plan — we do believe in a sense that they are behind schedule in what they were trying to accomplish in the Donbas," the official said.