US House of Representatives of Intelligence Committee Chairman Adam Schiff, leading the Trump impeachment process, said Friday that lawmakers would "accelerate" efforts on the investigation.
"We expect to announce additional testimony from relevant witnesses in the coming days and remain prepared to compel testimony through duly authorized subpoenas as appropriate", Schiff said in a letter to House members on Friday.
On Friday, Schiff updated colleagues that the committee has scheduled depositions "with Dr. Fiona Hill, former Senior Director on the National Security Council for European and Russian Affairs, who left the White House in August 2019; Deputy Assistant Secretary George Kent; Ambassador Gordon Sondland; and State Department Counselor T. Ulrich Brechbuhl".
Earlier on Friday, US Envoy to the European Union. Gordon Sondland, expressed readiness to testify next week in the impeachment probe, despite orders from the Trump administration to avoid cooperation.
The committee earlier released a series of text messages in which the US envoy questioned the White House's decision to withhold millions of dollars in military aid to Ukraine as Trump asked Ukraine to investigate allegations of corruption by former US Vice President Joe Biden.
Trump denies wrongdoing and accuses House Democrats of waging a political campaign against him.
House Democrats launched an impeachment inquiry into Trump’s 25 July telephone conversation with Ukraine President Volodymyr Zelensky based on a whistleblower complaint that Trump had solicited in a quid pro quo talk to assist in derailing the campaign of Democratic presidential nominee Joe Biden.
The White House has declassified what they claim is an unredacted transcript of the phone conversation, which does not contain signs that the US president overtly threatened to withhold financial assistance to Ukraine.