Ukraine's President Petro Poroshenko has said that only a referendum can decide whether Ukraine should be a federation or give autonomy to certain regions.

"The question of autonomy is one of constitutional change. And it will, of course, require another model of discussion, including a referendum," he told reporters at the Munich Security Conference.

"Today I am ready to put the question of federalization to a referendum, and I know the results. I am ready to put the question of an official language to a referendum, and I know the results," Poroshenko said.