The head of the US House Intelligence Committee has said it takes any witness intimidation "very, very seriously".

Adam Schiff was responding after President Donald Trump took aim at the country's former ambassador to Ukraine.

Marie Yovanovitch has been testifying against President Trump as part of his impeachment inquiry.

She was removed from her post in the spring after coming under attack from Mr Trump's personal lawyer, Rudy Giuliani.

Mr Trump is accused of abusing power by withholding aid for Ukraine - unless the country investigated his political rival, Joe Biden.

Mr Trump denies this.

The inquiry stems from a phone call between Mr Trump and Ukrainian President Volodymyr Zelenskiy on July 25th.

A White House memorandum suggests Mr Trump urged Mr Zelenskiy to work with Mr Giuliani and the US attorney-general to investigate Joe Biden.

Former US Ambassador to Ukraine, Marie Yovanovitch, testifies before the House Intelligence Committee on Capitol Hill in Washington | Image: Susan Walsh/AP/Press Association Images

In the call, Mr Trump raised unsubstantiated allegations that Mr Biden, the former US vice president and Democrat candidate in the 2020 election, sought to interfere with a Ukrainian prosecutor's investigation of his son Hunter.

Earlier this week, the inquiry heard from William Taylor, the top US diplomat in Ukraine.

He told the inquiry about a member of his staff who heard Mr Trump asking another senior diplomat about the investigations he wanted Ukraine to pursue.

"Following the call with President Trump, the member of my staff asked Ambassador Sondland what President Trump thought about Ukraine.

"Ambassador Sondland responded that President Trump cares more about the investigations of Biden, which Giuliani was pressing for", Mr Taylor said.

"At the time I gave my deposition on October 22nd, I was not aware of this information - I'm including it here for completeness.

"As the committee knows, I reported this information through counsel to the State Department's legal advisor - as well as to counsel for both the majority and the minority on the committee.

"It is my understanding that the committee is following up on this matter."

US President Donald Trump in the White House welcoming Turkish President Recep Tayyip Erdogan | Image: Douglas Christian/Zuma Press/PA Images

On Friday, Ms Yovanovitch told the committee she thought corrupt Ukrainians helped her downfall.

"What continues to amaze me is that they found Americans willing to partner with them and, working together, they apparently succeeded in orchestrating the removal of a US ambassador.

"How could our system fail like this? How is it that foreign corrupt interests could manipulate our government?

"Which country's interests are served when the very corrupt behaviour we have been criticising is allowed to prevail?

"Such conduct undermines the US, exposes our friends, and widens the playing field for autocrats like [Russian] President Putin.

"Our leadership depends on the power of our example and the consistency of our purpose. Both have now been opened to question."

Mr Trump attacked Ms Yovanovitch on Twitter as she testified.

Everywhere Marie Yovanovitch went turned bad. She started off in Somalia, how did that go? Then fast forward to Ukraine, where the new Ukrainian President spoke unfavorably about her in my second phone call with him. It is a U.S. President’s absolute right to appoint ambassadors.

— Donald J. Trump (@realDonaldTrump) November 15, 2019

He claimed: "Everywhere Marie Yovanovitch went turned bad. She started off in Somalia, how did that go?

"Then fast forward to Ukraine, where the new Ukrainian President spoke unfavourably about her in my second phone call with him.

"It is a US president's absolute right to appoint ambassadors."

Ms Yovanovitch was asked about this at the hearing in Washington, and said she found it "very intimidating".

"I actually think that where I've served over the years, I and others have demonstrably made things better for the US as well as for the countries that I've served in".

"I can't speak to what the president is trying to do, but I think the effect is to be intimidating".

Mr Schiff replied: "Well, I want to let you know ambassador that some of us here take witness intimidation very, very seriously".

Right now, President Trump is watching our hearing and tweeting baseless attacks against Ambassador Yovanovitch.

This is witness intimidation in real time. And we won’t stand for it. pic.twitter.com/2MngDNJUaw

— Adam Schiff (@RepAdamSchiff) November 15, 2019

Main image: US House Intelligence Committee Chairman Adam Schiff speaks on Capitol Hill in Washington | Image: Jim Lo Scalzo/AP/Press Association Images