Setting up a dramatic political showdown that threatens Trump’s presidency, House of Representatives Speaker Nancy Pelosi on Tuesday said the Democratic-led chamber was launching an official impeachment inquiry.

Pelosi directed six committees to proceed with investigations of the president’s actions.

The half-hour July 25 call between Trump and Ukrainian President Volodymyr Zelenskiy occurred after Trump had ordered the US government to freeze nearly $US400 million ($A592 million) in American aid to Ukraine.

The administration only later released the aid.

According to the Trump administration’s summary, released on Wednesday, Trump told Zelenskiy that Attorney General William Barr and Rudy Giuliani would speak to him about reopening a Ukrainian investigation into a Ukrainian gas company for which former US vice president Joe Biden’s son Hunter had served as director.

Biden is the frontrunner for the Democratic presidential nomination for the 2020 election.

“The other thing, there’s a lot of talk about Biden’s son, that Biden stopped the prosecution and a lot of people want to find out about that, so whatever you can do with the attorney general would be great,” Trump said, referring to Barr.

In the summary, Trump never explicitly tells the Ukrainian president that the US aid is contingent upon him investigating Biden.

However Trump emphasises the importance of American financial support before pressing him for action on Biden.

“I will say that we do a lot for Ukraine,” Trump said, adding that “the United States has been very, very good to Ukraine”.

According to the summary, Zelenskiy responds that Trump is “1000 per cent” right, and thanks Trump for “your great support in the area of defence” and expresses interest in making another US arms purchase.

In raising the Biden issue, Trump tells Zelenskiy he would have Giuliani – “a highly respected man” – and Barr call him.

“Biden went around bragging that he stopped the prosecution so if you can look into it. It sounds horrible to me,” Trump said.

Zelenskiy assures Trump that his next prosecutor general “will look into the situation”.

“I’m sure you will figure it out,” Trump tells him, according to the summary.

Zelenskiy then volunteers that the “last time I travelled to the United States, I stayed in New York near Central Park and I stayed at the Trump Tower”, one of the president’s businesses, according to the summary.

“I also want to ensure you that we will be very serious about the case and will work on the investigation,” Zelenskiy added.

The House inquiry could lead to articles of impeachment in the House, which could trigger a trial in the Senate on whether to remove Trump from office.

Pelosi said the notes of the call confirm that Trump engaged in behaviour that undermines the integrity of US elections, the dignity of presidency and American national security.

-AAP

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