Leaders from seven major industrial nations said Wednesday that a referendum to have Crimea split from Ukraine and join Russia would “have no legal effect” and called on Moscow to stand down.

Crimean Cossacks stand guard in front of the local parliament building on February 28, 2014 in Simferopol, Crimea, Ukraine's strategic peninsula. Pro-Russian activists flexed their muscles in in Crimea on Friday, swarming government buildings after Kalashnikov-toting men in fatigues descended on two key airports, as tensions mounted over the strategic Ukrainian peninsula. Hundreds of pro-Moscow protesters in Crimea's capital Simferopol massed outside the regional parliament, seized on February 27, 2014 by separatist commandos, as 50 others formed a barricade outside the Ukrainian presidency's local office, blocking its newly designated director from going inside. AFP PHOTO/ GENYA SAVILOV GENYA SAVILOV/AFP/Getty Images

Crimean Cossacks stand guard in front of the local parliament building on Feb. 28, 2014 in Simferopol, Crimea, Ukraine’s strategic peninsula (Getty Images)

The Group of Seven, or G-7, which includes Canada, France, Germany, Italy, Japan, the United Kingdom and the United States, challenged Russia to “to cease all efforts to change the status of Crimea contrary to Ukrainian law and in violation of international law.”

The statement from the group comes on the heels of Crimea’s parliament voting recently to join Russia and setting a final referendum vote for Sunday, further escalating the already volatile situation in that region.

The process for the referendum is “deeply flawed” and the presence of Russian troops in the area illigitimizes any upcoming decision to side with Moscow, the nations said. “For all these reasons, we would not recognise the outcome.”

Russia argues that it is only acting in the interest of a region that has close cultural and political ties. But if Moscow annexes the area, it would violate five bilateral and international agreements, including the United Nations charter, Reuters noted.

Leaders from the seven industrial nations also warned that any effort by Russia to absorb Crimea “could have grave implications for the legal order that protects the unity and sovereignty of all states.”

In its statement, the G-7 warned there would be further action against Russia if Moscow makes a move annex Crimea.

“Should the Russian Federation take such a step, we will take further action, individually and collectively,” the seven nations said.

The Group of Eight, the G-7 plus Russia, was supposed meet in Sochi in June, but the seven nations called off that meeting until further notice because of the situation in Ukraine.

The European Council and the European Commission contributed to Wednesday’s statement.

European Council head Hermann Van Rompuy, seven nation leaders “and I will in a new declaration call on Russia to cease all efforts to annex Ukraine’s autonomous republic of Crimea,” European Commission President Jose Manuel Barroso said in a tweet.

“Together with other G7 leaders, Van Rompuy and myself have strongly and unequivocally condemned this action on behalf of the EU,” Barroso said.

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