Updated: February 28, 2014 at 4:59 pm
"Any violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing," Obama declared. Such action by Russia would represent a "profound interference" in matters that must be decided by the Ukrainian people, he said.
As Obama prepared to speak late Friday in Washington, a spokesman for the Ukrainian border service said eight Russian transport planes had landed with unknown cargo in Crimea. Serhiy Astakhov told The Associated Press that the Il-76 planes arrived unexpectedly Friday and were given permission to land, one after the other, at Gvardeiskoye air base, north of the regional capital, Simferopol.
It's unclear whether the administration's threats to pull trade talks or cancel presidential travel will have any impact on Russia's calculations. Obama canceled a bilateral meeting with Russian President Vladimir Putin last year after Russia granted asylum to National Security Agency leaker Edward Snowden, though Obama still attended a separate international meeting in Russia.
Putin is scheduled to host the Group of Eight economic summit in June in Sochi, the site of the recently completed Winter Olympics. The administration official said the U.S. was in discussions about the summit with European partners and it was difficult to see how some of those leaders would attend if Russia had forces in Crimea.
The official was not authorized to discuss the situation by name and spoke only on condition of anonymity.