(CNN) A State Department official told lawmakers that Rudy Giuliani's attacks were part of a "campaign of lies" against the former Ukraine ambassador, according to a transcript released Thursday.

Deputy Assistant Secretary of State George Kent testified that President Donald Trump's personal lawyer's actions contributed to his decision not to speak out internally about Giuliani in the run up to the July phone call between Trump and the Ukrainian President. Kent, who oversees US policy on Ukraine, told lawmakers that he did not speak to anyone at State to express his concerns about Giuliani because he had previously been told to "keep my head down" after Giuliani attacked him by name.

"I did not, in part because after Giuliani attacked me, as well as (then-US ambassador to Ukraine Marie) Yovanovitch and the entire embassy, in his late May interview, I was told to keep my head down and lower my profile in Ukraine," Kent testified in October.

Kent's testimony provides new insight into how then-US special envoy to Ukraine Kurt Volker and US Ambassador to the European Union Gordon Sondland worked with Giuliani on Ukraine, as well as the reactions inside the State Department to Giuliani's efforts that Kent and others say ran counter to US foreign policy. The three coordinated a draft statement for Ukrainian President Volodymyr Zelensky to announce investigations into the 2016 election and Burisma, the company that hired former Vice President Joe Biden's son Hunter Biden.

Kent's testimony also sheds new light on instances where Volker appeared to press the Ukrainians to announce investigations if they wanted to secure a White House meeting, as well as Trump's desire for Zelensky to "say investigations, Biden, Clinton" in announcing an investigation. Kent testified that he believed there was a quid pro quo linking a meeting to the investigations -- bolstering the views of other key witnesses -- though he said that he didn't see US military aid to Ukraine as part of the equation.

Kent is one of three witnesses who will testify publicly next week when the House impeachment investigation into Trump and Ukraine shifts into the public phase. The deposition transcripts of Taylor, who will be testifying along with Kent on Wednesday, and Yovanovitch , who will appear publicly Friday, were released by House Democrats earlier this week.

In his deposition, Kent said that Volker told him in July that he was engaging with the President's lawyer because of Giuliani's "influence on the President in terms of the way the President thought of Ukraine."

Kent said he asked Volker why he would be reaching out to Giuliani, given Giuliani's public efforts to investigate former Biden and his attacks on Yovanovitch.

"And Kurt's reaction, or response to me at that was, well, if there's nothing there, what does it matter? And if there's something there, it should be investigated," Kent said. "My response to him was asking another country to investigate a prosecution for political reasons undermines our advocacy of the rule of law."

Volker told Kent that he felt it was worthwhile engaging with Giuliani because of his influence on the President's thinking about Ukraine.

"What I understood was Kurt was thinking tactically and I was concerned strategically," Kent said.

Kent said that he was warned by former White House aide Fiona Hill about Sondland's apparent "lies about conversations that occur in the Oval Office," and he said Sondland's "freelancing" on Ukraine caused concern inside the State Department.

"They were aware of the challenge of dealing with Ambassador Sondland who has a, I would say, track record of freelancing, would be one way of putting it, but working on issues other than the reason why he was sent to Brussels to work our relationship with the European Union," Kent testified.

'Investigations, Biden and Clinton'

Kent's testimony provided Democrats with corroboration of a key part of their impeachment case against the President: that Trump wanted Zelensky to announce an investigation that would help the President politically.

Taylor's testimony that Trump had told Sondland he wanted Zelensky to "go to a microphone" matched up with Kent's testimony about what Taylor had described to Kent in September.

"POTUS wanted nothing less than President to go to (a) microphone and say investigations, Biden, Clinton," Kent said, later adding that Clinton was shorthand for the 2016 election.

Kent, however, did not have as much insight into whether the investigation was tied to aid, as Taylor testified and Sondland revised his testimony to link together.

"That was not clear to me," Kent said. "I wasn't part of this exchange."

While Kent said he did not associate US security aid with the Ukraine investigations into Trump's political rivals, he testified that he did think the investigations were linked to a one-on-one meeting between Trump and Zelensky, though he said that was his "personal opinion" of the matter.

But he provided new details about conversations he witnessed between Volker and Ukrainian officials that shaped his views.

At an event called the Ukraine Reform Conference, Kent said Volker told him he would need to meet privately with Zelensky and would pull him aside.

"And he explained to me that the purpose of that private conversation was to underscore the importance of the messaging that (Zelensky) needed to provide to President Trump about his willingness to be cooperative," Kent said, though he did not know the details.

Later, Kent testified about an "awkward conversation" between Volker and Zelensky aide Andriy Yermak, relayed to him by Taylor, when Volker told Yermak he thought it would be inappropriate for the Zelensky administration to investigate former Ukrainian President Petro Poroshenko.

"And then Andriy Yermak said: What? You mean the type of investigations you're pushing for us to do on Biden and Clinton?" Kent told lawmakers.

Later, Kent said, when the conversation turned to the potential for Zelensky and Trump to meet, Volker said it was "important that President Zelensky give the message that we discussed before," Kent said, which he understood to be the public announcement of an investigation. But Taylor told Yermak "don't do that," according to Kent.

Giuliani's work in Ukraine dated back months

Kent testified privately before House lawmakers on October 15, and he appeared under subpoena despite State Department orders not to cooperate with Congress.

Kent explained in his testimony how Giuliani's work in Ukraine dated back months before the July phone call and its aftermath, including learning in January that Giuliani had been in touch with the State Department regarding the denial of a US visa for former Ukrainian Prosecutor General Viktor Shokin, and even attempted to call the White House as part of that effort.

Kent said that Shokin was "well and very unfavorably known" to the State Department, and the visa ultimately was not approved.

Kent also described Giuliani's relationship with former Ukraine prosecutor general Yuriy Lutsenko as "a classic, you scratch my back, I scratch yours, issue."

"Based on what I know, Yuriy Lutsenko, as prosecutor general, vowed revenge, and provided information to Rudy Giuliani in hopes that he would spread it and lead to her removal," Kent said. "I believe that was the rationale for Yuriy Lutsenko doing what he did."

Kent testified that Giuliani was "almost unmissable" starting in mid-March as the "news campaign or campaign of slander" against Yovanovitch and others unfolded, according to the transcript released Thursday.

He told lawmakers there were four storylines, all of which had no merit, that unfolded in both US and Ukrainian media.

The first story line involved attacks against anti-corruption actors in Ukraine and the US embassy, according to Kent. The second was "the 2016 cycle, allegations that somehow, somebody, whether it was Ukrainians or people at the embassy had animus towards Paul Manafort," he said. The third line of reporting was related to the Bidens, and the interconnectivity between Biden's role and pushing an anti-corruption agenda, and the presence of his son, Hunter Biden, on the board of the gas company Burisma, Kent said. And the fourth was alleging that certain organizations were funded by George Soros.

Kent testified that pressing Ukraine to investigate the Bidens and the Democratic National Committee servers "is not anti-corruption," and actually resembles a selective prosecution of political opponents. He said that Biden was promoting the "national interest" when he threatened to withhold US aid from Ukraine unless they fired the top prosecutor Shokin, but Trump was pursuing "partisan interest" in his push for an investigation.

But Kent was also critical of Hunter Biden's position on the Burisma board. He said he raised his concerns about Hunter Biden's position in 2015 and was told the vice president had "no further bandwidth" to deal with family-related issues, as his son Beau was dying of cancer at the same time.

'Unusual channels'

Internal State Department emails that were turned over to Congress showed that Kent rushed to the defense of Yovanovitch earlier this year when she was the target of attacks from Giuliani and other Trump allies. Top officials asked Secretary of State Mike Pompeo to defend Yovanovitch, but he stayed silent, and she was pulled from her post in May.

career diplomat since 1992, Kent is the deputy assistant secretary in the European and Eurasian Bureau, and oversees State Department activities for six countries, including Ukraine. Kent is one of 15 current and former Trump administration officials who have given closed-door depositions in the inquiry so far. His transcript is the sixth that the Democrats have released.

Kent's testimony explained how he saw the President's views on Ukraine being shaped. He recalled a conversation with Hill in May, in which they "talked about the change of attitude and approach towards Ukraine, and that was in the wake of meetings that President Trump had, a meeting with Viktor Orban, the leader of Hungary, as well as a call he had with Russian President Vladimir Putin in early May."

Kent's testimony explained how Sondland, Volker and Energy Secretary Rick Perry — who dubbed themselves the "three amgios" working on Ukraine — increased their role in Ukraine after they briefed the President following Zelensky's inauguration in May.

Kent said that the eventually, "our engagement with Ukraine shifted into, shall we say, unusual channels."

When the US security aid was frozen by the Office of Management and Budget, Kent described how there was "great confusion among the rest of us because we didn't understand why that had happened." Kent said Tim Morrison of the National Security Council, who also testified before Congress, led an effort to enlist Pompeo and Defense Secretary Mark Esper to personally lobby Trump to unfreeze the funds. The aid was eventually released on September 11, following calls with Republican lawmakers.

Kent was not on Trump's July 25 call, but he testified the readout he received was "different than any readout call that I had received."

The readout -- which came from Lt. Col. Alexander Vindman -- who also testified earlier this month, did not include specifics like the Bidens or Burisma, Kent said. But Vindman told him that "the conversation went into the direction of some of the most extreme narratives that have been discussed publicly."

"He actually said that he could not share the majority of what was discussed because of the very sensitive nature of what was discussed," Kent testified.

This story has been updated with additional developments Thursday.