Ukraine's richest man and the chief financier of deposed president Viktor Yanukovych on Sunday denounced Russia's incursion and called for Ukrainians to preserve their country's territorial integrity.
Russia's "recourse to force from outside is unacceptable. The crisis can only be resolved peacefully," said Rinat Akhmetov, one of the former president's closest allies.
"I call on all citizens to unite for a united and indivisible Ukraine. We must keep cool heads, not succumb to provocations and take well-considered decisions," Akhmetov said in a statement.
Like Yanukovych, Akhmetov comes from the pro-Russian region of Donetsk in eastern Ukraine, where his financial holding company System Capital Management is based.
Akhmetov, said by Forbes magazine to be worth more than $15 billion, was twice a member of parliament for Yanukovych's Regions Party.
On Saturday, the local council in Donetsk called for a referendum on whether to remain part of Ukraine following a large pro-Russian demonstration.