Washington suspended U.S. military collaboration with Russia in an indication of rapidly escalating tensions between the world's two largest nuclear powers.
The Defense Department tied its Monday announcement to developments in Ukraine, where Russian loyalists appeared to seize key government offices, airports and other facilities across the country's Crimean Peninsula.
"We have, in light of recent events in Ukraine, put on hold all military-to-military engagements between the United States and Russia," Pentagon spokesman Rear Adm. John Kirby told journalists on Monday. The decision extended to joint drills, bilateral exchanges between officials, preparatory gatherings and stops at each other's seaports, according to a news release from the Defense Department.
Russian President Vladimir Putin on Tuesday denied reports that soldiers with unmarked uniforms in Ukraine were under Moscow's command, but he added that Russia is lawfully entitled to deploy forces to the country in response to a request by deposed Ukrainian President Viktor Yanukovych, the Washington Post reported.
"All we did was reinforce the defense of our armed facilities" on Crimea, Putin said, without referencing the Russian armed presence now around Ukrainian military sites and vessels in waters surrounding the peninsula.
"[Russian bases] have been receiving threats because radicals, extremists were moving to Crimea," the Russian president added. "We hope we won’t be forced to do anything like that in eastern Ukraine."
Washington's envoy to the United Nations argued that Moscow had "many options short of military action" to meet its stated interests, including the aim of protecting Russians in Ukraine amid the country's current political unrest.
"Why choose military action when the consequences could be devastating?" Ambassador Samantha Power asked in a statement to the U.N. Security Council.
Kirby said the Pentagon is carefully watching regional developments in coordination with the State Department and other U.S. government offices, as well as partnered countries and NATO.
The spokesman said: "We call on Russia to de-escalate the crisis in Ukraine and for Russian forces in Crimea to return to their bases, as required under the agreements governing the Russia Black Sea Fleet."
He added that Washington had not altered its European and Mediterranean naval deployments in response to the developments in Ukraine.
"[U.S.] Navy units continue to conduct routine, previously planned operations and exercises with allies and partners in the region."