A senior U.S. official said that the "point in all of his calls, frankly, has been to underscore the complete illegitimacy of Russia's intervention in Crimea, in Ukraine, and to underscore the support of the United States for Ukraine's territorial integrity and its sovereignty."
The U.S. and its allies are collaborating to issue "strong national statements ... making clear that we all consider the Russian occupation of Crimea to be a violation of international law, a violation of Russia's obligations under the UN Charter and various other commitments, including the bilateral basing agreement with the Ukrainians."
The U.S., the official said, is committed to political, economic, and diplomatic efforts that fall short of American military intervention. The president is considering a range of response options that "include isolation, potential sanctions, and relationships between Russia and international institutions."
On Sunday, NATO's 28 members issued a strong statement that condemned Russia's military intervention into Ukraine.
G-7 members announced Monday that they would suspend their planned participation at the June Group of Eight meeting in Sochi, Russia.
"We, the leaders of Canada, France, Germany, Italy, Japan, the United Kingdom and the United States and the president of the European Council and president of the European Commission, join together today to condemn the Russian Federation's clear violation of the sovereignty and territorial integrity of Ukraine, in contravention of Russia's obligations under the U.N. Charter and its 1997 basing agreement with Ukraine."
The U.S., the official said, is "also looking with allies and partners at a broad range of options to curtail our economic and trade relationship" that will pressure Russia "to make it clear how we feel about this."
In addition to economic initiatives, the Obama administration is seeking the deployment of monitoring and observation teams, an initiative supported by Ukraine's parliament. On Monday, the State Department noted its appreciation for the OSCE's decision to deploy monitors to Ukraine "who can provide neutral facts, make a true assessment of the situation on the ground." The U.S. is also asking the UN to deploy monitors.
Secretary of State John Kerry is scheduled to arrive Tuesday in Kiev to confer with the Ukrainian interim government and with plans to convene a meeting with the parties of the Budapest Memorandum of 1994. Under the memorandum -- signed by Russia, the U.S., and the U.K. -- Ukraine is assured of protection from threats or use of force against its territorial integrity or political independence.
2014: The Year in Music [PHOTOS]