Vice President Pence's office on Wednesday flatly denied Ambassador to the European Union Gordon Sondland's testimony that the two had a conversation in Ukraine in which the latter raised concerns that aid had become linked to investigations sought by President Trump -- the matter at the heart of the impeachment inquiry.

Pence Chief of Staff Marc Short said in a statement that the purported conversation between him and Sondland “never happened.”

“The vice president never had a conversation with Gordon Sondland about investigating the Bidens, Burisma, or the conditional release of financial aid to Ukraine based upon potential investigations,” Pence said in his statement. “Ambassador Gordon Sondland was never alone with Vice President Pence on the September 1 trip to Poland. This alleged discussion recalled by Ambassador Sondland never happened.”

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Sondland on Wednesday morning said in his opening statement that he had spoken to Pence about the delay in military aid to Ukraine, voicing concern this was tied to investigations. Sondland said he believed the aid would not be released until Ukrainian President Volodymyr Zelensky's government announced an investigation concerning the Bidens.

“I mentioned to Vice President Pence before the meetings with the Ukrainians that I had concerns that the delay in aid had become tied to the issue of investigations,” Sondland said. “During the actual meeting, President Zelensky raised the issue of security assistance directly with Vice President Pence. The Vice President said he would speak to President Trump about it.”

Sondland added: “Based on my communications with Secretary Pompeo, I felt comfortable sharing my concerns with Mr. [Andriy] Yermak [an aide to Zelensky]. In a very brief pull-aside conversation, that happened within a few seconds, I told Mr. Yermak that I believed that the resumption of U.S. aid would likely not occur until Ukraine took some kind of action on the public statement that we had been discussing for many weeks.”

Sondland also made clear he never heard directly from Trump on such a quid pro quo.

The impeachment inquiry into Trump began when a whistleblower reported that the president had pushed Zelensky to launch a public investigation into the Biden family’s dealings in Ukraine—specifically, why former Vice President Joe Biden pressured former Ukrainian President Petro Poroshenko to fire a top prosecutor, Viktor Shokin, who was investigating Ukrainian natural gas firm Burisma Holdings.

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Hunter Biden worked for the Ukrainian gas company at the same time his father was leading the Obama administration's diplomatic dealings with Kiev.

Sondland told the House Intelligence Committee that he never heard Trump say that military aid to Ukraine was conditioned on a public announcement by the Ukrainian president that the country was investigating Democrats, but he added that it was clear that a meeting in the White House between Trump and Zelensky was conditioned on investigations.

He also said Trump never told him a White House meeting with the Ukrainian president would not happen without a public announcement. He heard that from Trump’s personal lawyer Rudy Giuliani.

Sondland said it was a personal guess that the military aid was being held up until an announcement, one that others eventually also made.

The Associated Press contributed to this report.