The annexation follows Sunday's contested Crimean referendum in which the Crimean parliament asked its citizens to vote on whether to remain part of Ukraine or to secede and join the Russian Federation. A reported 96 percent of the population voted in favor of annexation.
The Ukrainian government, joined by much of the international community, denounced the referendum as "illegal," asserting that such a vote was in violation of the Ukrainian constitution. Some questioned whether the votes were freely cast amidst a Russian occupation of Crimea.
On Thursday, U.S. President Barack Obama announced that he had signed a new Executive Order to further sanction Russia for its support of the "illegal referendum in Crimea, an illegitimate move by the Russians to annex Crimea, and dangerous risks of escalation including threats to Ukrainian personnel in Crimea and threats to southern and eastern Ukraine as well."