Hagel's spokesman, Rear Admiral John Kirby, told reporters today that Hagel expressed concern about Russian-influenced "irregular" military troops operating in eastern Ukraine.
And he said Hagel believes those irregulars are, at the very least, influenced by Moscow.
Kirby said Russian Defense Minister Sergei Shoigu expressed a "different view," but Kirby did not elaborate.
Hagel also was assured, twice during the conversation Monday, that Russia has no intention of invading Ukraine, Kirby said.