Russia agreed to refrain until Friday from taking over Ukrainian bases by force in Crimea, where voters on Sunday voted to break from Kiev and join Moscow.
Ukraine on Sunday declared it had reached a ceasefire agreement with the Russian Foreign Ministry and Crimean officials that will mean no incursions into Ukrainian military facilities in Crimea until week's end, the Daily Beast reported.
Crimea officially asked on Monday to join Russia after voters overwhelmingly approved a referendum on leaving Ukraine, Reuters reported. Russia's State Duma is anticipated to approve a bill permitting Crimea to become part of Russia "in the very near future," the speaker of parliament's lower house was reported by the state-controlled news agency Interfax to have said.
Russia's military occupation of Ukraine's Crimea Peninsula has brought East-West tensions to one of their most dangerous points since the end of the Soviet Union, though U.S. and European officials say military action is not likely to take place over the issue.
Still, in a throwback to the kind of rhetoric heard during the Cold War, a Russian television anchor handpicked by President Vladimir Putin made a clear nuclear war threat during his weekly program.
"Russia is the only country in the world that is realistically capable of turning the United States into radioactive ash," Russia news agency head Dmitry Kiselyov said.
President Obama spoke with Putin over the phone on Saturday about the situation in Crimea. The U.S. leader "reiterated that a diplomatic resolution cannot be achieved while Russian military forces continue their incursions into Ukrainian territory and that the large-scale Russian military exercises on Ukraine's borders only exacerbate the tension," a White House readout states.
European Union foreign policy chiefs on Monday approved seizing the assets and imposing travel bans on 21 Crimean and Russian individuals with ties to the secession movement in Crimea, the Associated Press reported.
The continued deterioration in U.S.-Russia relations could harm multinational efforts to stem weapons of mass destruction proliferation in Iran, Syria, North Korea and elsewhere, some experts warn.
"The U.S. and Russia are fundamental to the international communities' ability to work the diplomatic levers of many of the world's day-to-day flare-ups, and it would be very dangerous for this relationship to become undependable or 'out of service,'" a onetime State Department official told Defense News.