U.N. deputy chief Jan Eliasson will fly to Ukraine, where a threatened Russian invasion has risked sparking the worst crisis since the Cold War.

The world body's Secretary-General Ban Ki-moon ordered Eliasson to visit Ukraine after two emergency sessions of the U.N. Security Council that saw Western countries trade blame with Russia for the unfolding crisis in Ukraine.

"The deputy secretary-general will be personally apprised of the facts on the ground and will subsequently brief the secretary-general on the next steps the United Nations could take to support the de-escalation of the situation," Ban's spokesman said.