Kerry's trip comes as the U.S. and other Western nations weigh a response to Russia's military advance into Ukraine. Kerry has raised the possibility of issuing economic sanctions and visa bans, freezing Russian assets and levying trade and investment penalties.
The official says the U.S. now believes that Russia has complete operational control of the Crimea peninsula, a pro-Russian area of Ukraine, and has more than 6,000 forces in the region. The official said the U.S. is also watching for ethnic skirmishes in other areas of eastern Ukraine.
A second administration official indicated that the U.S. was not weighing military action to counter Russia's advances, saying the Obama administration's efforts were focused on political, economic and diplomatic options.
The officials were not authorized to publicly discuss the situation and insisted on anonymity.