William Taylor, the top U.S. diplomat in Ukraine, on Wednesday said that U.S. Ambassador to the European Union Gordon Sondland told a member of his staff in July that President Trump cared more about an investigation into former Vice President Joe Biden than he did about Ukraine.

Taylor described the conversation relayed to him last week by a member of his staff during his opening remarks at the first hearing in the House impeachment inquiry on Wednesday.

According to Taylor, the conversation took place on July 26, the day after a phone call between Trump and Ukrainian President Volodymyr Zelensky in which Trump raised investigations into the 2016 election interference and the Biden family. Taylor said his staffer, who he did not name, overheard a phone call between Sondland and Trump during which the president asked the EU ambassador about the investigations.

"Ambassador Sondland called President Trump and told him of his meetings in Kyiv. The member of my staff could hear President Trump on the phone, asking Ambassador Sondland about 'the investigations,'" Taylor said.

"Ambassador Sondland told President Trump that the Ukrainians were ready to move forward. 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 [Trump attorney Rudy] Giuliani was pressing for," he continued.

Taylor said that Sondland made the comments following a meeting with a top Zelensky aide, Andriy Yermak, in Ukraine. Taylor said he was not aware of the details when he testified behind closed doors in connection with the impeachment inquiry last month and that he was including it for "completeness."

"I reported this information through counsel to the State Department's Legal Adviser, 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," Taylor said.

Sondland, who testified privately before the committees before Taylor, has also corrected his remarks to say that he told Yermak during a meeting on Sept. 1 that aid to Ukraine would not likely flow until Kyiv made a public statement about pursuing investigations related to 2016 election interference and Burisma, a Ukrainian energy firm with ties to Hunter Biden.

Sondland has sought to distinguish the issue of Burisma from the Bidens, though other witnesses have connected the two. Trump specifically named Biden on the call with Zelensky in July. Sondland is due to testify publicly next Wednesday.

The Trump administration eventually released military aid to Ukraine, and Kyiv did not make a public statement about pursuing investigations sought by Giuliani and Trump.

Taylor is testifying on Wednesday as part of the first open hearing in House Democrats' impeachment inquiry. Trump has insisted he did nothing wrong in his interactions with Zelensky, describing the July 25 phone call as "perfect" and accusing Democrats of a partisan effort to damage him politically. Trump has said he wanted Ukraine to investigate "corruption" and that his comments had nothing to do with politics.

Taylor testified behind closed doors in connection with the inquiry on Oct. 22. His private testimony was released last week by the House committees leading the impeachment inquiry.

In his detailed opening remarks, Taylor described many of the interactions with Trump administration officials and other points he touched on during his prior testimony.

Taylor described an effort by the administration driven by Giuliani to leverage a White House meeting and aid to Ukraine to press Kyiv to launch investigations that could benefit Trump politically, emphasizing his concerns about it.

He reiterated his belief that "withholding security assistance in exchange for help with a domestic political campaign in the United States would be crazy" - echoing a remark he made in a text message to Sondland.

At the same time, Taylor also emphasized he wasn't taking sides - Republican or Democrat - during the impeachment hearing and was there only to relay the facts as he knows them.

"I want to emphasize at the outset that while I am aware that the committee has requested my test as part of impeachment proceedings, I am not here to take one side or the other," Taylor said at the beginning of his remarks.

The White House later dismissed Taylor and George Kent, the second State Department official testifying, as "bureaucrats with a foreign policy gripe" and said they offered no firsthand information.

"Dems star witnesses can't provide any first hand knowledge of any wrongdoing by @POTUS. Their own testimony contradicts the Dems false quid pro quo narrative. These are essentially two bureaucrats with a foreign policy gripe," White House press secretary Stephanie Grisham tweeted.

Taylor, a career State Department official who served in both Republican and Democratic administrations, came out of retirement earlier this year at the request of Secretary of State Mike Pompeo to lead the U.S. embassy in Ukraine.

Trump has criticized Taylor and the lawyer representing him as "Never Trumpers," at one point suggesting last month that Pompeo had made a mistake bringing him on at the State Department.

"NEVER TRUMPERS!" Trump tweeted earlier Wednesday morning before the impeachment hearing began.

"READ THE TRANSCRIPT!" he wrote, referring to the rough transcript of his call with Zelensky that has been released by the White House.

The White House said that Trump was working in the Oval Office and not watching the impeachment hearing on Wednesday.

Updated at 1:32 p.m.