Ukrainian acting President Oleksandr Turchynov told eastern regions gripped by a pro-Russian uprising that they would be courting catastrophe if they voted "yes" in a separatist referendum on Sunday.

Turchynov, who deems the vote in the Russian-speaking Donetsk and Luhansk regions illegal, urged the population to accept "round table" talks on greater autonomy. But, in reference to fighters who have seized police and government buildings, he said "terrorists" could not be included.

The vote, organized on a largely ad hoc basis with no clear control of authenticity of ballot papers or voter lists, could have serious consequences for Ukraine and relations between Moscow and the West. It risks turning isolated clashes into civil war.