"We are convening an emergency meeting of the United Nations Security Council on the humanitarian situation in Ukraine," Russian Ambassador to the U.N. Vitaly Churkin was quoted as saying.

Earlier on Tuesday, the Russian Foreign Ministry said the U.N. and the International Committee of the Red Cross expressed "readiness" to discuss its plan to deploy a "humanitarian mission" to Ukraine, which some consider to be a pretext for an invasion by Russian forces.  

Russia has significantly built up its troop presence along the Ukrainian border in recent weeks, according to U.S. officials, making it ready for a potential large-scale invasion of southeastern Ukraine if Russian President Vladimir Putin so chooses.

According to a report in The New York Times, Russia has nearly doubled its troop presence along the border, adding 17 battalions and 19,000 to 21,000 troops who now compose a "battle-ready force of infantry, armor, artillery, and air defense within a few miles of the border."