US Ambassador to the European Union Gordon Sondland, left, walks to a secure area of the Capitol to testify as part of the House impeachment inquiry into President Donald Trump, Monday, Oct. 28, 2019, in Washington. (Photo: AP)

House investigators are releasing more transcripts in the impeachment inquiry of President Donald Trump.

Democrats Tuesday released hundreds of pages of testimony from two top diplomats: Kurt Volker, the former special envoy to Ukraine, and Gordon Sondland, the US Ambassador to the European Union.

Both testified for hours behind closed doors about Trump’s interest in having Ukraine pursue investigations of Joe Biden and Democrats. The push came as the White House withheld military aid to the East European ally

Democrats say that’s an improper quid pro quo. Trump says he did nothing wrong.

The two diplomats were part of a pivotal May meeting with Trump at the White House that raised red flags. They also engaged in a text message chain about the administration’s actions toward Ukraine.

Three committees leading the House impeachment probe are asking White House acting chief of staff Mick Mulvaney to appear for a closed-door interview on Friday.

The panels on Tuesday wrote to Mulvaney requesting his appearance, saying they believe he has “first-hand knowledge” of President Donald Trump’s dealings with Ukraine.

In a televised news conference last month at the White House, Mulvaney appeared to acknowledge that Trump held up military aid to Ukraine partly for political reasons. He then later denied that he had said it.

Mulvaney is one of 13 witnesses that the Democrats have called to testify behind closed doors this week. It is unclear if he will show up since Trump has directed members of his administration not to cooperate.