US President Donald Trump's former adviser on Russia, Fiona Hill, has urged politicians in the impeachment inquiry not to promote "politically driven falsehoods" that cast doubt on Russia's interference in the 2016 US election.

In her testimony to the House of Representatives Intelligence Committee, Ms Hill said some members of the panel based on their questions and statements appear to believe that Russia and its security services did not conduct a campaign against the United States during the presidential race and that perhaps Ukraine did.

Some Republican members of the Democratic-led committee, which is leading the impeachment inquiry, have advanced a discredited conspiracy theory, promoted by President Trump and his political allies, that Ukraine, not Russia, interfered in the 2016 election.

"This is a fictional narrative that has been perpetrated and propagated by the Russian security services themselves," said Ms Hill, who until July served as the director for European and Russian affairs on the White House National Security Council.

"In the course of this investigation, I would ask that you please not promote politically driven falsehoods that so clearly advance Russian interests," she said.

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The hearing marks the fifth and last scheduled day of the House Intelligence Committee's public hearings in the impeachment inquiry.

The investigation is focused on President Trump's request in a 25 July phone call with Ukrainian President Volodymyr Zelenskiy that Mr Zelenskiy conduct two investigations that could harm Mr Trump's political adversaries.

The first involved Joe Biden, a leading contender for the Democratic nomination to face the president in next year's presidential election, and his son Hunter Biden, who had served on the board of Ukrainian gas company Burisma.

The second involved the discredited notion of Ukrainian interference in the 2016 election to harm President Trump's candidacy.

The inquiry is also examining whether Mr Trump's withholding of $391m in security aid to Ukraine, approved by the US Congress to fight Russia-backed separatists in the eastern part of the country, was meant to pressure Mr Zelenskiy to undertake the investigations.

US intelligence agencies and former Special Counsel Robert Mueller have determined that Russia interfered in the 2016 election with a campaign of hacking and propaganda intended to sow discord in the United States, boost Mr Trump's candidacy and harm his Democratic opponent Hillary Clinton.

Mr Mueller's team brought criminal charges against 12 Russian intelligence officers in the hacking effort, accusing them of covertly monitoring employee computers and planting malicious code, as well as stealing emails and other documents.

David Holmes, a member of staff at the US Embassy in Ukraine, also testified, as politicians seek to learn more about a 26 July phone call in which Mr Holmes said he overheard President Trump ask a senior US diplomat about the status of the investigations.

David Holmes

Mr Holmes testified that his work at the embassy started to become overshadowed in March by the actions of Mr Trump's personal lawyer, Rudy Giuliani, who was pushing Ukraine to carry out the two inquiries.

"I became aware that Mr Giuliani, a private lawyer, was taking a direct role in Ukrainian diplomacy," Mr Holmes said.

He added that he was "shocked" on 18 July when an official from the White House Office of Management and Budget announced that security assistance to Ukraine was being withheld.

"The official said the order had come from the president and had been conveyed to the office by Mr Mulvaney with no further explanation," Mr Holmes said, referring to acting White House Chief of Staff Mick Mulvaney.

Mr Holmes added that embassy officials spent the next weeks trying to determine why the aid was being held up.

Trump directed pressure on Ukraine, says US Ambassador

Yesterday, the US Ambassador to the European Union testified that President Trump directed a campaign of pressure on Ukraine to launch politically-motivated investigations.

Gordon Sondland has been accused of being centrally involved in efforts to pressure Ukraine to launch investigations into Mr Trump's political rivals.

He testified that he was following the president's orders and said "everyone was in the loop" including Vice President Mike Pence and Secretary of State Mike Pompeo.

Mr Trump, however, declared victory following the testimony, claiming to have been exonerated by Mr Sondland's evidence.

President Trump has denied wrongdoing, verbally assailed witnesses, and described the proceedings as a "witch hunt."

He also says he does not remember the call with Mr Sondland.

But, speaking to reporters as he left for Texas, Mr Trump, holding a notebook with notes written in marker, quoted Mr Sondland's closed-door deposition earlier this month in which the ambassador described a phone call in which the president had told he he did not want a quid pro quo.

He also reiterated his point in a tweet, writing "I WANT NOTHING! I WANT NOTHING! I WANT NO QUID PRO QUO! TELL PRESIDENT ZELENSKY TO DO THE RIGHT THING!"

Additional Reporting Brian O'Donovan