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The Group of 7 say they won't recognize the outcome of a referendum that would peel Crimea from Ukraine and allow it to join Russia. In a statement released Wednesday, the seven nations — Japan, Canada, France, Germany, Italy, Britain, and the United States — called on Russia to "cease all efforts to change the status of Crimea," warning that a referendum would be "contrary to Ukrainian law and in violation of international law."

"Any such referendum would have no legal effect," a statement from the G7 read. "Given the lack of adequate preparation and the intimidating presence of Russian troops, it would also be a deeply flawed process which would have no moral force."

The referendum is due to take place Sunday.