Donald Trump has described allegations by an intelligence whistleblower as “just another political hack job”.
The complaint, which his administration has refused to let Congress see, remains shrouded in mystery but is “serious” and “urgent,” the government’s intelligence watchdog said.
A number of US news outlets claim the allegations involve the Republican president’s communications with a foreign leader while others say it involved “multiple acts”.
A report in the Wall Street Journal claims the US president repeatedly pressured his Ukrainian counterpart Volodymyr Zelenskiy to investigate Democratic presidential candidate Joe Biden’s son.
However, Mr Trump has dismissed the matter, insisting he did nothing wrong.
“I have conversations with many leaders. It’s always appropriate,” he told reporters during an Oval Office meeting with Australian Prime Minister Scott Morrison.
“At the highest level always appropriate. And anything I do, I fight for this country.”
Mr Trump was asked if he discussed Mr Biden during the call with President Zelenskiy, and he answered: “It doesn’t matter what I discussed.”
He then urged the media “to look into” Mr Biden’s background with Ukraine.
House Speaker Nancy Pelosi said Mr Trump faces “serious repercussions” if the reports are accurate and said the whistleblower’s complaint raises “grave, urgent concerns for our national security”.
The intelligence community’s inspector general appeared before the House Intelligence committee behind closed doors on Thursday but declined, under administration orders, to reveal the substance of the complaint.
However, he did say the matter involves the “most significant” responsibilities of intelligence leadership.
House Intelligence Chairman Adam Schiff has vowed to mount an extensive investigation into the scandal.
“Come hell or high water, that’s what we’re going to do.”
Among the materials Democrats have sought is a transcript of Mr Trump’s 25 July call with Mr Zelenskiy. The whistleblower’s complaint was made on 12 August.
Joseph Maguire, the acting director of national intelligence, is understood to have consulted with the Justice Department in deciding not to transmit the complaint to Congress.
Mr Maguire has refused to discuss details of the whistleblower complaint, but he has been subpoenaed by the House panel and is expected to testify publicly next Thursday.