EU Council President Donald Tusk has begun a three-day visit to Ukraine.
Together with President Petro Poroshenko, he commemorated the victims of the Ukrainian revolution five years ago.
From 18 to 20 February 2014, more than 100 people were killed in heavy fighting on Maidan Square.
At a speech to the parliament he said:
"I can reiterate that Europe will never recognise the Russian annexation of Crimea and will not drop the sanctions unless Russia fulfils its commitments. Nor will the EU accept any acts of violence in the Sea of Azov. I will do everything in my power to ensure that the EU remains united in this respect."