Ukrainian President Petro Poroshenko has called on Ukrainians to unite so as not to "become a very easy prey for the enemy in a hybrid war."

"The record teaches us that, when we lapse into amnesia, we become a very easy prey for the enemy in a hybrid war. We have learned to defend our land, and we have built one of the most powerful and certainly one of the most patriotic and strongest armies on the continent. The enemy realized that attempts to directly attack our boundaries have no prospects," Poroshenko said in unveiling a monument to Hetman Ivan Mazepa in Poltava on Saturday.

The enemy has now switched to a different tactic, that is, "financing and supporting fifth columns, which are destroying Ukrainian unity," Poroshenko said.

"Politicians should also take history lessons today and, most importantly, for the future. I'd stress once again that a lack of unity has repeatedly been fatal to Ukraine. This is a more than obvious conclusion from events of both the 18th and the 20th century," Poroshenko said.