Three United States House of Representatives committees said on Monday they had launched “a wide-ranging investigation” into reports that President Donald Trump, his lawyer Rudy Giuliani and possibly others allegedly pressured Ukraine’s government to assist Trump’s re-election campaign by targeting former Vice President Joe Biden.

The Democratic chairmen of the House Intelligence, Oversight and Foreign Affairs committees wrote to the White House and the State Department seeking records related to what they described as efforts to “manipulate the Ukrainian justice system”.

Trump and some of his fellow Republicans have questioned whether it represented a conflict of interest that Hunter Biden, the son of Joe Biden, a presidential candidate, had served on the board of Burisma, a Ukrainian gas company.

Giuliani reportedly met a top representative of the Ukrainian president and urged him to look into two issues: Hunter Biden’s past role at Burisma, and whether Ukrainian officials sought to harm Trump’s 2016 presidential campaign.

“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 chairmen wrote in a joint statement.

“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 reelection campaign, and the White House and the State Department may be abetting this scheme,” they continued.

The letter noted that Trump “threatened to withhold more than $250m in security assistance” to Ukraine.

“If the president is trying to pressure Ukraine into choosing between defending itself from Russian aggressions without US assistance or leveraging its judicial system to serve the ends of the Trump campaign, this would represent a staggering abuse of power,” the chairmen said.

White House aides did not immediately respond to a request for comment on the announcement of the inquiry by the Democratic-led House committees.

Giuliani told the New York Times last month that he was acting as a private citizen when he spoke to the Ukrainian presidential representative. He also said the State Department was aware of the meeting, but would not comment on whether Trump knew about his efforts.