Russian forces are becoming increasingly frustrated by what the United States believes is "viable" Ukrainian resistance, a U.S. defense official said on Saturday.
"We know that they have not made the progress that they have wanted to make, particularly in the north. They have been frustrated by what they have seen is a very determined resistance," the official said, without providing evidence.
"It has slowed them down," the official added.
(Reporting by Phil Stewart and Idrees Ali; Editing by Daniel Wallis)
