The US is working with global allies to ensure that sanctions imposed on Russia cost Moscow dearly.
David Cohen, US Treasury Undersecretary for Terrorism and Financial Intelligence, said: "We are moving in a strong and systematic way to maximise the cost on Russia ... while minimising to the extent possible the spillover on other economies."
The Obama administration is working on new sanctions that would be imposed on Russia should it dramatically ramp up aggression against Ukraine.
New measures could include preventing elections from taking place in much of Ukraine or recognising another separatist referendum.
European Union foreign ministers added 13 people to their visa ban and asset freeze list over Ukraine's crisis.
Well that’s the voting over, and no surprises so far. A ‘Yes’ vote claimed to be 89% in Donetsk, and suddenly Ukraine is no more.
Nearly 90 percent of voters in eastern Ukrainian region voted for self-rule, the head of the separatist election commission said.