The US State Department warned American citizens on Friday of possible military clashes along the Russian-Ukrainian border and potential anti-American activities in Russia as Crimea prepares to vote Sunday on whether to join Russia.
In a "travel alert," the State Department said it had no information of military conflict inside Russia as a result of regional tensions or of any threat specific to US citizens.
"However," it said, "all US citizens located in or considering travel to the border region ... should be aware of the potential for escalation of tensions, military clashes (either accidental or intentional) or other violence."
In the worst East-West confrontation since the Cold War, Moscow shipped more troops into Crimea on Friday and repeated its threat to invade other parts of Ukraine in response to violence the night before in Donetsk.
EU diplomats will choose from a list of possible Russian targets for sanctions on Sunday, as pro-Moscow authorities who have taken power in Crimea hold a vote on whether to join Russia.