(CNN) Gordon Sondland , the American envoy to the European Union, was acting at President Donald Trump's instruction in his dealings with Ukraine, and Sondland said that the President told him Ukrainian President Volodymyr Zelensky "must announce the opening of the investigations," according to the closed-door deposition of a former National Security Council official.

Former NSC official Tim Morrison testified that he had heard from Sondland that US aid to Ukraine was conditioned on the country announcing an investigation into former Vice President Joe Biden and his son Hunter Biden.

Morrison's testimony will only fuel questions about Sondland's closed-door interview, which has been called into question based on the testimony others have given about his conversations with Trump. Sondland is scheduled to testify publicly before the House Intelligence Committee on Wednesday.

House impeachment investigators also released Saturday the transcript of Jennifer Williams , an aide to Vice President Mike Pence, who listened into the July 25 call along with Morrison. While Morrison did not take specific issue with the content of Trump's call with Zelensky, both aides described their concerns as they listened to Trump discussing political investigations.

Morrison's testimony also added additional detail explaining how the call ended up on a highly secure server outside of normal channels.

Morrison, who is scheduled to testify publicly on Tuesday, described how Sondland was a "problem" as he operated in what previous witness testimony described as irregular foreign policy channels . And he recalled Sondland speaking directly to Trump about the investigations and the military aid.

"He related to me he was acting -- he was discussing these matters with the President," Morrison said.

After a September 1 meeting between Zelensky and Vice President Mike Pence in Warsaw, Morrison testified he saw Sondland from across the room speaking with a top aide to Zelensky. Afterward, Sondland walked over to Morrison to tell him what he'd said.

"He told me that in his -- that what he communicated was that he believed the—what could help them move the aid was if the prosecutor general would to go the mic and announce that he was opening the Burisma investigation," Morrison said, referring to the Ukrainian energy company that hired Joe Biden's son Hunter Biden.

Later, Morrison recounted another conversation with Sondland where the investigations arise -- only this time Trump was more directly involved.

Morrison said on September 7, Sondland informed him about a telephone call he'd held with Trump. "He told me he had just gotten off the phone with the President," Morrison said, adding: "He told me, as is related here in Ambassador Taylor's statement, that there was no quid pro quo, but President Zelensky must announce the opening of the investigations and he should want to do it."

Morrison testified he had concerns that what Sondland told him was exaggerated or inaccurate. But he said that "as often as I had time to," he worked to confirm Sondland's communications with Trump, and he never discovered an instance where they had not communicated.

Morrison, Hill said Sondland was 'a problem'

Morrison said Sondland was a concern for his predecessor, former White House Russia expert Fiona Hill , who is also scheduled to testify publicly next week.

"She described Ambassador Sondland as a problem," Morrison said, recounting a conversation they had about Sondland. "We both discussed that Ukraine was not in the EU, which led to the follow-on question of, why is he involved in Ukraine? And, as I mentioned, she mentioned Burisma, which I nearly did not know what that was."

Morrison explained their concern: "It was less about his role in Ukraine and more about how he conducted himself. He did not participate in the process. So we are very process-oriented on the NSC; we have a way we do things that works. And so when people come in and get involved in issues and they're not of that process, it creates risk."

Morrison pointed the finger at Sondland for having "chiefly led" the irregular diplomatic process, which incorporated Trump's personal attorney Rudy Giuliani. Morrison said this irregular channel differed from the "normal process" that the US government uses for foreign policy.

"There was the normal process, where decision-making went through the duly appointed personnel, whether that's the Chief of Mission, Ambassador Taylor, (former US special envoy to Ukraine Envoy Kurt) Volker, the appropriate personnel from the Departments of State and Defense and Energy and intelligence agencies and so forth, as we normally do business," Morrison said. "And there was this second track, chiefly led by Ambassador Sondland, where Rudy Giuliani's name would come up."

Morrison also testified that Sondland spoke to Trump by phone the morning of his July 25 phone call with Zelensky.

"Ambassador Sondland emailed me and several other White House staff to inform us that he had spoken to the President that morning to brief him on the call," Morrison said.

Morrison testified that he voiced his worry after the call to the top NSC lawyers out of concern the call could leak. He wanted to ensure the top attorneys, not their deputies saw the call, he said.

He explained that his concern about it leaking was because he "didn't necessarily fully understand how everybody would use it" but he worried it would wind up "politicizing Ukraine" and cost bipartisan support for the country.

"I was concerned about how the Ukrainians would internalize that," Morrison said.

Morrison said he also had "concerns" about the Lt. Col. Alexander Vindman's judgment in regards to policy. Morrison's comments could put Vindman -- who will testify publicly next week about his concerns with the July call -- further in the crosshairs of Trump, who called Vindman a "never Trumper" before his deposition.

New details about Pence's role

Williams told House investigators "the mention of those specific investigations" during the July Trump-Zelensky call "seemed unusual as compared to other discussions with foreign leaders."

"I believed those references to be more political in nature and so that struck me as unusual," she said, later adding that she found the requests to be more specific to Trump's "personal political agenda."

Prior to the July call, Williams said she had not heard discussion in the Office of the Vice President or the White House of CrowdStrike or the Democratic National Committee server, Ukrainian interference in the 2016 election, or investigating Biden and his son Hunter. There is no evidence of wrongdoing by either Biden in Ukraine.

Williams was asked if on the call Pence gave Zelensky any advice on how to approach Trump when they met at the forthcoming United Nations General Assembly meeting. Williams said Pence told Zelensky, "President Trump would be eager about President Zelensky's progress in his reform agenda."

When asked by House investigators to define "reform agenda" Williams said, "on anticorruption reforms, on reforming the judiciary, and the legislative action that his administration was undertaking, but there was no discussion of any specific investigations."

Williams also provided details on Pence's September 1 meeting with Zelensky and highlighted how concerned the Ukrainian President was about US military aid being withheld, saying it was the first question he asked Pence when the press left their bilateral meeting in Warsaw, Poland. In his response, Pence said he wanted to hear about the progress of "reforms" in Ukraine so he could relay them to Trump.

"The VP responded by neatly expressing our ongoing support for Ukraine, but wanting to hear from President Zelensky, you know, what the status of his reform efforts were that he could then convey back to the President," Williams said of Pence, according to a transcript of her deposition.

Transcript mistakenly moved

Morrison provided new details on the moving of the transcript between the President and Ukraine's leader to a highly classified server, saying it was a "mistake".

During his deposition, Morrison relayed senior NSC lawyer John Eisenberg's explanation that Eisenberg's executive secretary mistakenly put it in the highly classified system. Morrison acknowledged that he and Eisenberg had previously discussed that access to the transcript should be restricted.

Upon finding it the transcript in the special server, they asked themselves, "how did it get on there?"

Morrison continued, "John (Eisenberg) related that he did not ask for it to be put on there, but that the Executive Secretariat staff misunderstood his recommendation for how to restrict access."

Eisenberg was subpoenaed to testify by House Democrats, but he did not appear for a deposition last month.

Bolton and Trump met over withheld aid, Morrison said

Trump's former national security adviser John Bolton met with Trump in August in an attempt to persuade him to release US military aid to Ukraine, according to the transcript of Morrison's testimony.

The meeting was not previously reported, but apparently failed to sway Trump over the release of the aid.

Morrison said after Bolton met with the President, Bolton relayed back that Trump "was not yet ready to approve the release of the assistance."

Democrats have invited Bolton to testify in private , but his attorney said he won't appear without a subpoena.

This story has been updated.