Congressional Democrats are pressing their demands for full disclosure of a whistleblower’s complaint about Donald Trump and intensified calls for impeachment.

The president again insisted he did nothing wrong in a conversation with Ukraine’s leader which is at the centre of the complaint.

Republican legislators remained largely silent amid reports that the president pressured Ukraine’s leader to help investigate political rival Joe Biden at the same time the White House was withholding 250 million dollars in aid to the eastern European nation.

Mr Trump acknowledged the phone call and said he did not want to give money to Ukraine if there were corruption issues.

His comments raised further questions about whether he improperly used his office to pressure the country into investigating the former US vice president and his family as a way of helping his own re-election prospects.

“It’s very important to talk about corruption,” Mr Trump told reporters at the United Nations. “If you don’t talk about corruption, why would you give money to a country that you think is, is corrupt?”

He has sought, without evidence, to implicate Mr Biden and his son Hunter in the kind of corruption that has long plagued Ukraine.

Hunter Biden served on the board of a Ukrainian gas company at the same time his father was leading the Obama administration’s diplomatic dealings with Kiev. Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice president or his son.

Volodymyr Zelenskiy
Volodymyr Zelenskiy (Efrem Lukatsky/AP)

The matter is under new scrutiny following the whistleblower’s mid-August complaint, which followed Mr Trump’s July 25 call with Ukraine President Volodymyr Zelenskiy. The person who filed the complaint did not have firsthand knowledge of the call, according to a source.

Legislators are demanding details of the complaint, but the acting director of national intelligence has refused to share that information, citing presidential privilege.

Later on Monday, Mr Trump denied telling the Ukraine president that his country would only get US aid if it investigated Mr Biden’s son. “I didn’t do it,” he said, adding that he hoped a transcript would be made available to demonstrate his innocence.

Senate Democratic leader Chuck Schumer called on Republican majority Leader Mitch McConnell to investigate the whistleblower’s complaint. In a letter, he said the Republicans’ “see no evil, hear no evil” attitude towards the president’s actions “is unacceptable and must change”.

“In the face of this dire warning and the Trump administration’s effort to cover it up, the Republican-led Senate has remained silent and submissive, shying away from this institution’s constitutional obligation to conduct oversight,” Mr Schumer wrote.

Democrats remained divided on moving forward with an effort to impeach Mr Trump. House speaker Nancy Pelosi has resisted calls for impeachment for other allegations of transgressions, and is sticking with her position that Congress must not start formal proceedings unless the American public demands it.

However, she said on Sunday that unless the administration provides more information to Congress by a scheduled Thursday hearing at the intelligence committee, its officials “will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation”.

More than half the House Democrats have said they support impeachment, and more are expected this week to publicly favour such an investigation, but others worry it is too politically divisive and would only alienate more centrist voters.