Ukrainian President Petro Poroshenko has pledged to return Crimea to Ukrainian control.

"The Ukrainian state will regain control over this temporarily occupied territory. I am not saying that this will be a simple thing to do which we will go through quickly. But this will happen by all means. Together we will build a new Crimea, where the rights and interests of Crimea's indigenous population and of all residents irrespective of their ethnicity, language and religion, will be guaranteed," Poroshenko said in an appeal to the Ukrainian people issued in Kyiv on Monday.

Poroshenko said that on February 23, 1918 "Moscow Bolsheviks in Crimea ... executed the outstanding Crimean Tatar activist, co-founder and Chairman of the National Kurultai, the Mufti of Muslims of Crimea, the author of the Crimean Tatar national anthem.

"A year ago, the events, which are difficult for any civilized person to understand in the 21st century, took place. Humanity witnessed the cynical actions aimed at seizing Crimea - an integral part of Ukraine. The so-called referendum announced and conducted simultaneously with a large-scale invasion of the Crimean land by Russian military, was nothing more than a farce designed to cover up the open aggression of Russia against Ukraine," the statement reads.

"The Ukrainian state will not under any circumstances recognize the results of this null act, which defied international law and Ukraine's national legislation," Poroshenko said.

"Ukraine will never give up its sovereign right to Crimea and will defend the rights of the people who live there. The Ukrainian leadership, politicians and civil society have reached a complete consensus on this. We enjoy absolute support for this course from other states and from international organizations," Poroshenko said.

Poroshenko delivered his speech in the Ukrainian, Russian, and Crimean Tatar languages.