Donald Trump has insisted he did nothing wrong in a "nice" call with Ukraine's president - hours after he appeared to confirm that he had discussed former vice-president Joe Biden with the foreign leader.
The moves are the latest twist following a whistleblower complaint that reportedly alleged the US president pressured Ukrainian President Volodymyr Zelensky to probe Mr Biden and his son Hunter.
Mr Trump weighed in on Twitter after a full day of attacks against Mr Biden, the current front-runner for the Democratic presidential nomination, by Trump administration officials and allies .
They demanded investigations of Mr Biden and his son Hunter despite a lack of evidence of wrongdoing, as Seung Min Kim and Felicia Sonmez, of 'The Washington Post' reported.
Mr Trump repeated those claims on Twitter, again without any evidence, writing, "Sleepy Joe Biden, on the other hand, forced a tough prosecutor out from investigating his son's company by threat of not giving big dollars to Ukraine.
"That's the real story!"
The 'Washington Post' Fact Checker has previously found no merit to allegations that Mr Biden used the threat of withholding loans to force out a prosecutor who had investigated a natural gas company that hired Hunter Biden.
Mr Trump's latest claims come as Democratic calls for impeachment intensify over the extraordinary whistleblower complaint first reported the 'Post' last week.
Although the intelligence community's inspector general found the complaint credible and urgent enough to disclose to congressional committees, Mr Trump has repeatedly insisted he did nothing wrong and his administration has refused to share details of the complaint with Congress.
On Twitter, he apparently referred to a 'Wall Street Journal' report that he had asked Mr Zelensky eight times to investigate the former vice-president.
"Now the Fake News Media says I 'pressured the Ukrainian President at least 8 times during my telephone call with him,'" Mr Trump tweeted.
"This supposedly comes from a so-called 'whistleblower' who they say doesn't even have a first hand account of what was said. More Democrat/Crooked Media con . . ."
He then apparently cited a story in which Ukrainian Foreign Minister Vadym Prystaiko told a local television station "I think there was no pressure" from Mr Trump on the call with Mr Zelensky.
"Breaking News: The Ukrainian Government just said they weren't pressured at all during the 'nice' call," Mr Trump tweeted.
Mr Zelensky has not commented but hours earlier, Mr Trump had appeared to confirm with reporters outside the White House that he had brought up Mr Biden and his son on the call.
"The conversation I had was largely congratulatory, was largely corruption, all of the corruption taking place, was largely the fact that we don't want our people, like Vice-President Biden and his son, creating to the corruption already in the Ukraine," he said.
"And Ukraine, Ukraine's got a lot of problems."
Democrats say asking Ukraine to find damaging information on a potential 2020 rival could amount to another attempt to involve a foreign power in US elections.
Intelligence agencies concluded Russia interfered in the 2016 election to help Mr Trump, a claim he denies.
The story is likely to dominate Mr Trump's coming week at the United Nations General Assembly in New York, where he's scheduled to meet Mr Zelensky tomorrow.
Secretary of State Mike Pompeo claims he has not seen the whistleblower complaint or news reports about it but, appearing on a number of television shows, preferred to raise questions about whether the former vice-president acted properly.
"I do hope that if vice-president Biden engaged in behaviour that was inappropriate, if he had a conflict of interest or allowed something to take place in Ukraine, which may have interfered in our elections in 2016, I do hope that we get to the bottom of that," Mr Pompeo said.
There is no evidence that Mr Biden played any role in any election interference efforts by foreign governments in 2016.
Since the spring, Rudy Giuliani, Mr Trump's personal attorney, has pushed the Ukrainians to pursue two investigations.
He wants one inquiry into a gas tycoon who had Hunter Biden on his board and another into his claim Democrats colluded with Ukraine to release information on jailed former Trump campaign chairman Paul Manafort. (© Washington Post)