WASHINGTON — In a closed-door hearing Thursday on Capitol Hill, former U.S. envoy to Ukraine Kurt Volker sought to distance himself from President Donald Trump’s efforts to get the Ukrainian government to investigate former Vice President Joe Biden and his son Hunter, according to a copy of his testimony obtained by NBC News.

In an opening statement ahead of more than nine hours of congressional questioning, Volker said that he was not on the president’s July 25 phone call with Ukrainian President Volodymyr Zelenskiy and that he was not aware of Trump's request regarding Biden and his son until a summary of the transcript was released on September 25. He also said he did not believe there was a connection between security aid for Ukraine and promises to investigate unproven allegations against the Bidens.

Volker also told Congress that he cautioned the Ukrainians not to get involved in the 2020 U.S. elections and said that he felt Trump was being fed negative information about Ukraine, particularly from Trump’s personal lawyer Rudy Giuliani.

Late Thursday night, House Democrats released pages of text messages between Volker and two other diplomats that showed the diplomats working to persuade Ukraine to publicly commit to investigating the Bidens and linking the inquiry to an official White House visit for Zelenskiy.

“Several times I cautioned the Ukrainians to distinguish between highlighting their own efforts to fight corruption domestically,” Volker said, “and doing anything that could be seen as impacting U.S. elections.”

Volker, who retired from his post at the end of September, said that he “did not perceive” the issue of the Bidens and the withholding of aid to be connected. He said that he pressed the administration on “how important it was to keep the security assistance moving.”

Volker also told Congress that he was becoming concerned that the president was being fed “a negative narrative” about Ukraine, including by Trump’s personal lawyer, Rudy Giuliani.

“He was clearly receiving other information from other sources, including Mayor Giuliani, that was more negative, causing him to retain this negative view,” Volker said.

Volker also said that Giuliani had insisted that Zelenskiy mention the energy company that Hunter Biden worked for, Burisma, and the 2016 election in a speech he was to deliver on ending corruption, But, he maintained that a draft of the speech he was shown appeared to be “perfectly reasonable” even though it didn’t mention either topic.

Giuliani, according to Volker, continued to push back.

“We had a further conversation with Mayor Giuliani, who said that in his view, the statement should include specific reference to Burisma and 2016,” Volker told Congress. Volker added that there was no mention of Vice President Biden in his conversations.