Ukrainian President Petro Poroshenko has called for tougher punishments for separatism.

"I think we should toughen punishments for separatist statements, let alone actions, in the process of decentralization, and these criteria should be clearly stated in the law so that people are afraid to even think about it," Poroshenko said during the first meeting of the constitutional commission in Kyiv on Monday.

"Ukraine paid and now pays a very high price" to maintain its unity, sovereignty and territorial integrity, he said.