Ukraine's Petro Poroshenko, set to be the new president after today's election, said he would never recognise Russia's "occupation of Crimea" and ruled out negotiating with separatists.
Asked about relations with Russia, he said the "sovereignty and territorial integrity" of Ukraine were paramount for him.
The confectionery tycoon also ruled out negotiations with pro-Russian separatists in the east of the country until they put down their weapons.
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The prime minister was shouted at as she left the scene of the tragedy in which at least 79 people died.
Father-of-six Makram Ali, 51, was already receiving medical treatment as the attack unfolded. He died from multiple injuries, police say.
A review of how police and security services dealt with the latest terror attacks in the UK is to be launched, Amber Rudd has announced.