G7 leaders warned Russia on Wednesday to "cease all efforts to change the status of Crimea" or face "further action, individually and collectively."
The statement issued by the White House in Washington came in response to Crimea's parliament endorsing moves to join Russia and making preparations for a referendum among local residents on Sunday (pictured).
The G7 group includes Canada, France, Germany, Italy, Japan, the United Kingdom, the United States, the European Council and the European Commission. In 1998 it added Russia to form the G8.
The G7 leaders said they would not recognize the outcome of the referendum, which they said "would have no legal effect."
The economic grouping described plans for Sunday as a "deeply flawed process which would have no moral force" because of the presence of presumed Russian troops on the Ukrainian Black Sea peninsula.
Instead, the leaders called on Russia to withdraw its forces in Crimea, begin talks with Ukraine, and allow international observers into the region.
Aside from affecting Ukraine's territorial integrity, an annexation of Crimea could have "grave implications for the legal order that protects the unity and sovereignty of all states," the G7 said.
The grouping said such a move would violate five different bilateral and international agreements.
"We ... urge Russia to join us in working together through diplomatic processes to resolve the current crisis," the G7 added.
Yatsenyuk to meet Obama
President Barack Obama was scheduled to meet visiting Ukrainian Prime Minister Arseniy Yatsenyuk at the White House on Wednesday.
Russia's cultural ministry said Wednesday more than 100 leading Russian arts figures, including conductor Valery Gergiev, had signed an open letter in support of President Vladimir Putin's policy on Ukraine and Crimea.
ipj/mz (dpa, Reuters, AFP)