Obama: International law violations will 'cost' Russia
13 March 2014 Last updated at 10:07 GMT
US President Barack Obama has welcomed Ukraine's interim prime minister to the White House and pledged to "stand with Ukraine" in its dispute with Russia.
He warned Russian President Vladimir Putin the international community "will be forced to apply costs" if Russia does not remove its troops from Crimea.
The BBC's North American editor Mark Mardell reports.