US President Donald Trump (R) leaves the White House in Washington D.C., the United States, on Nov. 6, 2019. (Photo by Ting Shen/Xinhua)

The first open impeachment hearings into US President Donald Trump will begin next week, the congressman leading the probe said on Wednesday, as the investigation heads into a highly anticipated public phase.

William Taylor, Washington's top diplomat to Ukraine, and deputy assistant secretary of state George Kent are scheduled to testify on November 13.

People will be able to see "the degree to which the president enlisted whole departments of government in the illicit aim of trying to get Ukraine to dig up dirt on a political opponent," said House Intelligence Committee Chairman Adam Schiff.

In a closed-door deposition, Taylor bolstered the principal accusation against Trump that the president abused his office by withholding military aid to blackmail Kiev into launching investigations that could help him politically.

Kent, who heads the European and Eurasian bureau at the State Department, expressed concerns about White House efforts to remove the then-ambassador to Ukraine, Marie Yovanovitch.

Yovanovitch herself told investigators she was ousted because Trump's personal lawyer Rudy Giuliani and others wanted her out of the way as they conducted Ukraine policy outside traditional diplomatic channels. She is scheduled to appear on November 15.

Schiff has already begun releasing transcripts of private witness testimony but it is widely believed that the trio's appearance at public hearings could have a more dramatic impact on the US public.

The Capitol Hill hearings will be broadcast live as lawmakers from both parties and trained staff question witnesses, many of whom the White House has sought to discredit.

Schiff said that moment in the fast-moving inquiry had ­arrived, and that US people would be able to hear the accounts of potential abuse of power directly from witnesses who were caught up in the scandal.

The hearings will let the US people "evaluate the witnesses for themselves, to make their own determinations about the credibility of the witnesses, but also learn firsthand about the facts of the president's misconduct," Schiff said.

An anonymous whistle-blower complaint in September highlighted potential abuse of power by the president when he telephoned Ukraine's leader and asked him to investigate former vice president Joe Biden, Trump's potential 2020 election rival.

The complaint led Democrats to launch their impeachment inquiry, which has led to an avalanche of witness testimony from current and former diplomats or administration officials who have largely corroborated the whistle-blower's account. Trump has attacked the complaint as "phony" and has demanded the whistle-blower's identity be revealed.