German Chancellor Angela Merkel has stepped up her criticism of Russia, saying the country has "exploited Ukraine's weakness instead of acting as a partner for stability."
Speaking in the German parliament, the Chancellor warned that if Russia continues its path, it would be "a catastrophe not just for Ukraine and the EU, but also for Russia."
She said that EU leaders are ready to "take further action" if Russia continues to destabilise the situation.
"The territorial integrity of Ukraine cannot be called into question," she said.
Mrs Merkel said the situation in Ukraine's southern region of Crimea was not comparable to the case of Kosovo in the Balkans.
Barack Obama warned Russia that the West will be forced to apply a cost to Moscow if it fails to change course in its dispute with Ukraine.
The ballot paper that the people of Crimea will use in Sunday's referendum was published today
Vitali Klitschko's visit to the eastern city of Donetsk is clearly an attempt to try to ease the divisions with Ukraine.