The U.S. and the six other world leaders on Wednesday called on Moscow to halt all efforts to promote the annexation of Ukraine's Crimea region to Russia, which they argued are in “violation of international law” and would have no impact because other countries would not recognize it.

Ignoring warnings from President Obama and other world leaders, Russian forces this week advanced further into the Crimean peninsula ahead of a March 16 referendum vote in the region on whether to join the Russian Federation.

Members of the G-8 group of world leaders, minus Russia, issued a joint statement Wednesday in an attempt to send a clear and united message to Russian President Vladimir Putin.

“We, the leaders of Canada, France, Germany, Italy, Japan, the United Kingdom, the United States, the president of the European Council and the president of the European Commission, call on the Russian Federation to cease all efforts to change the status of Crimea contrary to Ukrainian law and in violation of international law,” the leaders said, referring to themselves as the G-7.

“We call on the Russian Federation to immediately halt actions supporting a referendum on the territory of Crimea regarding its status in direct violation of the Constitution of Ukraine,” they added.

The March 16 referendum, they said, would be a violation of international law and Ukraine's sovereignty and territorial integrity. If Russia continues to push for the referendum, the G-7 leaders said they would “take further action, individually and collectively.”

“Any such referendum would have no legal effect,” they said. “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. For all these reasons, we would not recognize the outcome.”

The statement also echoed previous exhortations to Putin by Obama, British Prime Minister David Cameron and other world leaders to reverse course in Crimea.

The leaders urged Russia to “de-escalate the conflict in Crimea and other parts of the Ukraine immediately, withdraw its forces back to their pre-crisis numbers and garrisons, begin direct discussions with the Government of Ukraine, and avail itself of international mediation and observation offers to address any legitimate concerns it may have.”

“We, the leaders of the G-7, urge Russia to join us in working together through diplomatic processes to resolve the current crisis and support progress for a sovereign independent, inclusive and united Ukraine,” they said.

The leaders also reminded Russia that they have suspended participation in any activities related to preparation of the G-8 meeting planned to take place in Sochi, Russia in June until Moscow changes course “and the environment comes back to where the G-8 is able to have a meaningful discussion.”