The audiotape of a July 2019 phone call shows former US President Donald Trump's then-lawyer Rudy Giuliani pressuring Ukrainian officials to investigate baseless allegations about Trump's 2020 election rival Joe Biden, CNN reported on Monday.

CNN said it had obtained the audio of the call between Giuliani, US diplomat Kurt Volker, and Andriy Yermak, a senior adviser to Ukrainian President Volodymyr Zelenskiy which it said was the precursor of a Trump-Zelenskiy call which was at the centre of Trump's 2019 impeachment.

In the call, Giuliani said he wanted Zelenskiy to say he was putting a prosecutor in charge and...