In a phone call with Foreign Minister Sergey Lavrov Saturday, Secretary of State John Kerry “made clear that continued military escalation and provocation in Crimea or elsewhere in Ukraine, along with steps to annex Crimea to Russia would close any available space for diplomacy, and he urged utmost restraint," the state department reported. Warning shots meanwhile prevented OSCE observers from entering Crimea. Lavrov had earlier said that the crisis in Ukraine was "created artificially for purely geopolitical reasons." He confirmed that Russia had contacts with Ukraine's interim government but said Kiev was beholden to the radical right.

Friday, Lavrov warned that “hasty and reckless steps capable of causing harm to Russian-American relations – particularly…  sanctions, which would hit the United States like a boomerang.”

After President Obama held a round of talks with allied leaders, French president Francois Hollande said they discussed new measures against Russia if it failed to defuse the crisis by withdrawing its forces sent to Crimea.