That control is evident as Russia has maneuvered approximately 6,000 airborne and naval forces "with considerable materiel" into Crimea. So far, there is no evidence of Russian military in eastern Ukraine but, the official added "we're watching very carefully."
Russia's military intervention into Ukraine coincides with an on-going Russian military exercise that Russian President Vladimir Putin ordered on February 26.
Meanwhile, Ukraine continues to exercise what President Barack Obama has referred to as commendable restraint. The senior official said that "The Ukrainians, by and large, have stayed in base," at Sevastopol and, "In some cases, they've actually locked their weapons up."
When asked whether Obama is considering a military option in Ukraine, the senior official responded that the focus remains on political, economic, and diplomatic efforts.
"So I don't think we're focused right now on the notion of some U.S. military intervention. I don't think, frankly, that would be an effective way to de-escalate the situation."