KIEV, April 21 (Reuters) - Incumbent Ukrainian President Petro Poroshenko on Sunday conceded he had been soundly defeated in a run-off vote by comedian Volodymyr Zelenskiy and would be leaving office next month, but said he did not plan to quit politics altogether.

Ukraine entered uncharted political waters on Sunday after an exit poll showed Zelenskiy, a comedian with no political experience and few detailed policies, had easily won enough votes to become the next president of a country at war. (Reporting by Kiev Bureau Writing by Andrew Osborn Editing by Matthias Williams)