President Obama called a host of world leaders to discuss military tensions in Ukraine, White House officials said Saturday.
Obama spoke by phone with leaders Britain, France, Italy, Lithuania, Latvian and Estonia during a weekend trip to Key Largo, Fla.
They also consented on the formation of a group to lead direct talks between Russia and Ukraine to de-escalate unrest, the White House said in a statement.
"The leaders rejected the proposed referendum in Crimea as a violation of Ukraine’s constitution and underscored that all decisions about the future of Ukraine must include the government in Kyiv," the statement continued. "The leaders made clear that Russia’s continued violation of international law will isolate it from the international community."
U.S. and European officials have introduced sanctions against Russia after troops from the country attempted to take control of Ukraine's peninsula.
Russian leaders have denied responsibility for the situation, arguing that the troops that are in Crimea are not officially members of their military.
-This story was updated with new information at 2:15 p.m.