US President Barack Obama imposed sanctions on 11 Russians and Ukrainians on Monday blamed for Russia's military incursion into Crimea, including two top aides to Russian President Vladimir Putin.
Obama's order freezes any assets in the United States and bans travel into the country of 11 people named as responsible for the Russian move into Ukraine's Crimea region.
Among those sanctioned were ousted Ukraine President Viktor Yanukovich and Putin aides Vladislav Surkov and Sergei Glazyev.
The European Union also will impose travel bans and asset freezes on 21 Russian and Ukrainian officials, it was announced Monday.
The U.S. sanctions came in an executive order signed by Obama a day after Sunday's Crimea referendum aimed at allowing Russia to annex the region, a vote that the United States says was illegal and will never be recognized by Washington. The administration announced plans for sanctions earlier this month but had not named the individuals until Monday.
"Today's actions send a strong message to the Russian government that there are consequences for their actions that violate the sovereignty and territorial integrity of Ukraine, including their actions supporting the illegal referendum for Crimean separation," the White House said.
A senior Obama administration official said there was "concrete evidence" that some ballots in the Crimea referendum arrived in some Crimean cities pre-marked.