WASHINGTON (Reuters) - A White House employee testified Tuesday in a closed-door hearing before the three commissions investigating President Donald Trump's parliamentary trial over his "controversial" call with Ukraine's new president, Volodymyr Zelinsky.

The employee, a US Army officer named Alexander Findman, who works for the White House, is an expert on Ukraine's National Security Council, testifying after he was part of a small group of people charged with hearing the July 25 call between Trump and Zelinsky that caused To launch investigations aimed at prosecuting the president.

The officer plans to tell investigative committees that he was troubled by President Trump's demand that Ukraine investigate an American citizen, and that if Kiev responds to it, it would undermine US national security.

"I don't think it was appropriate to ask a foreign government to investigate an American citizen, and I was worried about the implications of the US government's support for Ukraine," Vendman said.

In a July 25 call, Trump asked his counterpart Zelinsky to investigate the activities of his opponent and potential rival Joe Biden and his son in Ukraine.

The revelation came after a complaint from a secret US intelligence informant said Trump had withheld US aid from Kiev to pressure the Ukrainian president to heed his request to investigate the activities of Joe Biden and his son.

"There is a lot of talk about Biden's son, and that Biden has stopped the investigation, and many people want to know more about it," Trump said in the call. "It would be great to have an investigation."

Trump has proposed to his Ukrainian counterpart to cooperate with his lawyer Rudy Giuliani and US Attorney General Bill Barr.

Findman (left) working as White House expert on Ukraine on National Security Council (US Press)

Accountability and details
Findman will be the first White House official to testify about Trump's controversial call that led to historic accountability.

Findman's statement reinforces the testimony given by former National Security Council President Fiona Hill and the US charge d'affaires in Kiev Bill Taylor.

Taylor said in a closed-door testimony that the US ambassador to the European Union, Gordon Sundland, had clearly told him that President Trump had linked the release of financial aid to Ukraine with Kiev's announcement of an investigation targeting Hunter Biden's son. Joe Biden who was a board member of a Ukrainian company.

"Sundland told me that everything was arranged by a declaration of this kind, including assistance," he said in a 15-page statement published in the Washington Post.

Democrats in the House of Representatives saw Taylor's testimony as evidence that the suspicions that led them to initiate impeachment proceedings against Trump were unfounded.

Loyalty and concern
Findman, whose family fled the Soviet Union when he was three and who describes himself as an immigrant and nationalist, insists he has no partisan bias, stressing that he is driven by allegiance to the Constitution and the country.

"It is my sacred duty and honor to come forward to defend our country regardless of party or politics," he said.

According to the Washington Post, Vendman will confirm in his statement that he had no direct contact with President Trump, noting that he was not a whistleblower whose complaint helped spark an investigation into the impeachment.

He did not know who had reported what had been regarded as abuses by the President, and he did not feel comfortable predicting it.

Despite being removed from the White House, Findman has become deeply concerned about the way the president and some of his top advisers are manipulating Ukraine's policy to discredit Biden's potential rival.

Cooperation in return
The US officer said that Trump had expressed his desire to work with President Zelinsky after his election, and invited the White House, noting that the Ukrainians felt that the meeting with Trump "crucial" to strengthen US support in the Russian aggression.

But this US support is tied to the expected testimony. In a July 10 meeting, US Ambassador to the European Union Gordon Sundland said that to ensure a meeting with Trump, the Ukrainians "must investigate the 2016 elections and Biden," he said. Borisma is a Ukrainian natural gas company that has controversially used Biden's son to serve on its board.

Findman said Sundeland's remarks were inappropriate and that the request to investigate Biden and his son had nothing to do with national security.