Russian advance slowed by Ukrainian resistance and logistical setbacks, U.S. defense official says

The Russian forces invading Ukraine have faced more resistance than the U.S. believes Russia anticipated, a senior defense official said Sunday morning. The Russian forces have advanced toward three cities, including Kyiv, but have not yet captured a city since invading. 

"The Ukrainians are putting up a very stiff and brave and heroic resistance, but we are only in Day Four, and I would be reluctant to provide an estimate of how many more days there are and what those days are going to look like," the senior defense official said. 

The U.S. Defense Department estimates about two-thirds of the combat power Russia had arrayed around Ukraine's borders have now been committed inside Ukraine. That leaves about one-third that have yet to enter the country, which is a significant amount of power still at the ready.