The White House has declared a freeze on assets of 11 Russian officials linked to the political push for Crimea's independence from Ukraine and possible annexation by Russia.
The Obama administration announced the sanctions Monday following the European Union, which designated 21 officials from Russia and Ukraine for travel bans and trade sanctions.
The moves came in response to Crimea's declaration of independence from Ukraine Monday and it plans to apply to become part of Russia. Crimea's regional assembly declared independence for the region after a referendum on Sunday indicated voters' overwhelming support for joining the Russian Federation.
In addition to responses from the U.S. and the European Union, NATO released a statement Monday calling the vote "illegal and illegitimate." It said the vote violates the Ukrainian constitution and international law, and added that the circumstances under which the referendum was held were "deeply flawed and therefore unacceptable."
Despite objections from the international community, a delegation of Crimean lawmakers is traveling to Moscow Monday to discuss additional procedures required to become part of the Russian Federation.
Ukraine's parliament has approved a partial mobilization of reservists in response to the crisis.
Crimea's election chief announced Monday that nearly 97 percent of the voters cast ballots supporting secession and a move to join Russia. However, those opposed to the move had been advised to boycott the referendum.
Crimea's pro-Moscow leader, Sergei Aksyonov, announced that his government will formally apply on Monday to join the Russian Federation.
In Kyiv, Ukraine's interim Prime Minister Arseniy Yatsenyuk called the Moscow-backed Crimea vote "a circus spectacle" directed at gunpoint by Russia.
An earlier White House statement said no decision should be made about the future of Ukraine without the Ukrainian national government.
It also said the presidential election planned for May 25 will provide a legitimate opportunity for all Ukrainians to make their voices heard on the future of their country.
Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on Sunday agreed to push for Ukrainian constitutional reforms for power sharing and decentralization as a solution to the crisis.
In Kyiv, Ukraine's acting defense minister told reporters that Ukraine and Russia have agreed on a truce in Crimea until March 21.
Sunday's vote came a day after Russian forces seized a natural gas facility just outside Crimean territory. The Ukrainian Foreign Ministry called the move "a military invasion by Russia."
Ukraine provides the peninsula with all of its water and energy needs, and some analysts say the seizure may be aimed at ensuring the peninsula's energy requirements are met in the event Kyiv were to cut off supplies.