This is Harris' highest-stakes foreign trip yet. She will meet some 13 heads of state to discuss the threat posed by Russia, and will speak at the Munich Security Conference.
A full-scale invasion is not a certainty. But if it happens, experts say the effects of sanctions, energy market disruptions and cyberwarfare could reach everyday Americans.
The outage impacted the website of the Ukrainian Defense Ministry and the Armed Services as well as two large Ukrainian banks, Privatbank and Oschadbank.
The two leaders spoke by phone for roughly an hour after the State Department ordered most of its embassy staff in Kyiv to leave. U.S. officials are concerned a Russian invasion is imminent.
Officials warn that an attack could result in the deaths of tens of thousands of soldiers and civilians, while millions of Ukrainian refugees would be left to flee, likely to nearby Poland.
New satellite images show the buildup of Russian forces and equipment along Ukraine's borders with western Russia, Belarus and Crimea — including new tents, an indicator that troops may be present.