Donald Trump’s alleged efforts to pressure the government of Ukraine to assist his 2020 re-election campaign are being investigated by Democrats on Capitol Hill.

As the party outlined a series of steps it hopes will take its impeachment investigation forward, three committees of the House of Representatives said they were probing alleged efforts by Mr Trump and his personal lawyer, Rudy Giuliani, to pressure Ukraine to influence the 2020 race in the US by launching an inquiry into whether Joe Biden acted wrongly in order to help his son in a business deal.

The Democratic chairmen of the house intelligence, oversight and foreign affairs committees wrote to the White House and state department seeking records related to what they described as efforts to “manipulate the Ukrainian justice system”.

The announcement in Washington followed a series of reports that Mr Giuliani, the former New York mayor who has been advising Mr Trump on legal matters, has been pressuring Ukraine’s president, Volodymyr Zelensky, to open proceedings into claims made by Republicans that Mr Biden acted unfairly to help his son, Hunter, in business dealings.

Mr Giuliani had been liaising with prosecutors in Kiev appointed by Mr Zelensky’s predecessors, to look into the company Hunter Biden worked for, and the oligarch who owned it.

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This summer, the New York Times reported that Mr Giuliani held a face-to-face meeting in Madrid, in addition to a series of phone calls, with representatives of the incoming president, and that his efforts to influence domestic decisions in Ukraine included threats about the future of US military aid to the country.

Mr Giuliani, claiming to have been acting as a private individual and not in any formal White House-designated role, was hoping Ukraine would step up its investigations into two matters. Firstly, he wanted to look into whether Ukrainian officials took steps during the 2016 presidential election to damage Mr Trump’s campaign, the newspaper reported.

He also wanted it to press ahead with enquiries into Mr Biden’s 2016 actions as vice president, when he threatened the allegedly corrupt administration in Kiev with the withholding of $1bn in United States loan guarantees, and to investigate if Ukraine’s leaders did not dismiss the country’s top prosecutor, who had been accused of turning a blind eye to corruption in his own office.

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Mr Giuliani told the newspaper he had “strongly urged” the Ukrainian official, Andriy Yermak, a close ally of Mr Zelensky, to “just investigate the darn things”. He said he could not determine whether his actions would interfere in relations between the countries.

“I can’t really evaluate that – whether my involvement in it makes it worse or better,” he said. “I can’t see how advocating for an investigation of two alleged crimes puts too much pressure on them, other than to do the right thing.”

“A growing public record indicates that, for nearly two years, the president and his personal attorney, Rudy Giuliani, appear to have acted outside legitimate law enforcement and diplomatic channels to coerce the Ukrainian government into pursuing two politically-motivated investigations under the guise of anti-corruption activity,” the three Democrats – Adam Schiff, Elijah Cummings, Eliot Engel – said in a joint statement on Monday.

They added: “As the 2020 election draws closer, president Trump and his personal attorney appear to have increased pressure on the Ukrainian government and its justice system in service of president Trump’s re-election campaign, and the White House and the state department may be abetting this scheme.”

There was no immediate response to the accusations from Mr Trump or the White House.

The move came after another Democratic-controlled House committee, the judiciary committee, announced it was examining steps to formalise its investigation to determine whether to impeach Mr Trump.

The panel, which hopes to determine whether to recommend Mr Trump’s impeachment to the full house by the end of the year, will meet on Thursday to consider a resolution that would open the door to the more aggressive questioning of witnesses at hearings and allow the White House to respond in writing to evidence and testimony.

The five-page measure also sets procedures for reviewing sensitive material, including grand jury evidence in closed-door sessions.

“The adoption of these additional procedures ... will help ensure our impeachment hearings are informative to congress and the public, while providing the president with the ability to respond to evidence presented against him,” congressman Jerry Nadler said in a statement.

While now more than half of Democratic members of congress say they support impeachment, the leadership, under house speaker Nancy Pelosi, has sought to avoid such a move in the belief it would energise the president’s base ahead of the 2020 election and put off independent voters. Polls suggest there is only modest support among the public for impeachment.

Earlier this year, special counsel Robert Mueller reported that his two-year investigation into Russia’s alleged interference in the 2016 election, and possible collusion with the Trump campaign, found no evidence of collusion. He said investigators were unable to clear the president of claims of obstruction of justice, and attorney general William Barr decided there would be no indictment of Mr Trump.