(CNN) Two White House officials told lawmakers the "blatant" push for politically motivated investigations from President Donald Trump left "no ambiguity" what the Ukrainians needed to do to secure a highly sought meeting — and the effort was coordinated by acting White House chief of staff Mick Mulvaney , according to deposition transcripts released Friday.

The testimony of National Security Council Ukraine expert Lt. Col. Alexander Vindman and former White House Russia expert Fiona Hill provides new details on the discussions inside the White House ahead of the July 25 call between Trump and Ukrainian President Volodymyr Zelenksy, in which Trump asked the Ukrainians to investigate former Vice President Joe Biden and Burisma, he Ukrainian natural gas company that hired Hunter Biden. The officials say they were told that effort was directed by Mulvaney, putting the Ukraine scandal squarely into the office of the President's top aide.

Vindman and Hill testified that US Ambassador to the European Union Gordon Sondland told Ukrainian officials in meetings on July 10 they would have to open an investigation to secure the White House meeting. Sondland told them he was acting at the direction of Mulvaney, who on Friday defied a congressional subpoena and did not appear for a deposition.

"Ambassador Sondland, in front of the Ukrainians, as I came in, was talking about how he had an agreement with Chief of Staff Mulvaney for a meeting with the Ukrainians if they were going to go forward with investigations," Hill testified.

She told Congress the suggestion alarmed then-national security adviser John Bolton, who "immediately stiffened" and ended the meeting.

Vindman said there was "no ambiguity" what Sondland was asking of the Ukrainians.

"On the 10th of July ... it became completely apparent what the deliverable would be in order to get a White House meeting. That deliverable was reinforced by the President," Vindman told lawmakers in his closed-door deposition last month. "The demand was, in order to get the White House meeting, they had to deliver an investigation. That became clear as time progressed from how this thing unfolded through the 10th all the way through the conclusion."

The depositions of Hill and Vindman add to House impeachment investigators' growing body of evidence that the push for Ukraine to investigate the 2016 election and Burisma was conditioned on a one-on-one meeting between Trump and Zelensky and the release of $400 million in US security aid that was frozen by the White House. Hill and Vindman provided new details on what the Ukrainians were told in the run-up to the July 25 call and how the White House handled the fallout from the call when the transcript was placed on a more secure server than normal.

House impeachment investigators released Vindman and Hill's deposition transcripts on Friday ahead of public impeachment hearings that will begin next week. The committees have now released transcripts from eight of the 15 depositions they have conducted.

Both Vindman, who was on the July 25 call with Zelensky, and Hill expressed significant concerns about the call itself. Vindman reported his concerns to National Security Council attorney John Eisenberg, while Hill testified she was "shocked" at Trump's request for investigations into his political rivals.

"It was pretty blatant," Hill said. "I found that I couldn't really explain that away with an alternate explanation."

Acting White House Chief of Staff Mick Mulvaney answers questions in during a briefing in October at the White House in Washington.

Giuliani's role in testimony

Hill testified behind closed doors last month that she was instructed by Bolton to take her concerns about the role Trump's personal attorney Rudy Giuliani was playing in Ukraine to National Security Council attorneys. Bolton told her to make clear he was "not part of whatever drug deal Sondland and Mulvaney are cooking up on this," Hill testified.

Hill said the TV in Bolton's office was always on, usually tuned to Fox. "And often when I was in the office, Giuliani would be on the television, and you know, Ambassador Bolton would put on the sound to hear what he was saying," Hill said.

Vindman testified that the Ukrainians asked him in the spring "for advice on how to respond to Mr. Giuliani's advances, meaning his call to undertake these -- what would come across as partisan investigations." Vindman said he recommended to Zelesnky not to get involved in US domestic politics.

When the July 10 meeting occurred with the Ukrainian delegation, Energy Secretary Rick Perry "laid out all of these talking points" about working with Ukraine to tackle corruption in the energy sector, Hill said. Bolton said that was encouraging and suggested they could start thinking about a meeting between Trump and Zelensky, urging the Ukrainians to deal with the State Department and with Perry on that.

That was when, Hill testified, Sondland "did a redirect" of the conversation.

"He was basically ... countermanding what Ambassador Bolton had just said. In other words saying, I actually have, you know, some completely separate agreement about a meeting, you know, kind of you're stonewalling kind of thing," Hill said.

After Bolton ended that meeting, Sondland went with the Ukrainians into a separate meeting. Hill said that Vindman was upset and uncomfortable at the conversation that unfolded.

"That's also because it was in front of Ukrainians, that it was basically Ambassador Sondland getting very annoyed that he already had an agreement with the chief of staff for a meeting between the Presidents on the basis of these investigations," she said.

'So my impression is that they were under pressure'

Hill left the National Security Council in the days before the July 25 call. Vindman, who is still working at the National Security Council, testified that he drafted "talking points" ahead of Trump's call with Zelensky, and that he was also listening in from the Situation Room. Those talking points did not include anything about investigations into the 2016 election, the Bidens or Burisma, Vindman said.

The NSC aide testified that the call solidified for the Ukrainians the "official role" that Giuliani was playing.

"There were concerns about (how Giuliani) .... could be undermining the consensus policy. But frankly, up until that call, you know, in certain regards he was acting as a private citizen advancing his own interests to a certain extent," Vindman said. "It wasn't until that call that it became, that he was pulled into kind of an official role."

While much of the focus on the quid pro quo has been over the $400 million in security aid, Vindman said that the July 25 call was "all about getting the bilateral meeting," because the Ukrainians were unaware at that point the aid was frozen.

Vindman said he was first aware of the hold on Ukraine aid by July 3, and later learned that it came from Mulvaney's office. He said that when the Ukrainians learned the aid had been held up, he they asked whether it was true and "what do we need to do?"

"So my impression is that they were under pressure," Vindman testified.

Vindman said that he had raised concerns about the July 25 call to NSC lawyers, and that the process that was used for placing the call transcript on a highly secure server was abnormal. Vindman has proposed edits to the rough transcript that was released by the White House — adding references to Burisma and recordings of Biden — that were not ultimately included in the White House's release. But Vindman testified that he believed there was no "malicious intent" behind his proposed edits being left out, saying he agreed that the White House's rough transcript was a "very accurate" depiction of the call.

This story has been updated with additional developments and will continue to update Friday.