Ukrainian President Volodymyr Zelenskiy has said there was "no blackmail" in a phone call with US President Donald Trump that helped spark an impeachment inquiry.

Mr Zelenskiy said he only learned after their July 25 phone call that the US had blocked hundreds of millions of dollars in military aid to Ukraine.

Mr Trump asked Mr Zelenskiy during the call to investigate Democratic rival Joe Biden, and Congressional Democrats believe Mr Trump was holding up the aid to use as leverage to pressure Ukraine.

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Mr Zelenskiy said he thought the call would lead to an in-person meeting with Mr Trump and wanted the American leader to come to Ukraine.

Mr Zelenskiy is giving an all-day "press marathon" amid growing questions about his actions as president.