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“The U.S. and Europe are finalizing measures to deepen and broaden our sanctions across Russia’s banking, energy, and defense sectors," he said.

Obama added that the support that NATO allies and other international countries are providing to Ukraine is "a testimony to how seriously people take the basic principle that big countries can't just stomp on little countries."

Read more on Obama's speech on ABC News.

Reach Supervising Executive Producer Shilpa Nagesh here. Follow her on Twitter here.