US President Donald Trump said Saturday that the White House would probably release a transcript of a second call with Ukrainian President Volodymyr Zelenskiy on Tuesday.
"We have another transcript coming out which is very important," Trump told reporters at Joint Base Andrews before leaving for a visit to Tuscaloosa, Alabama. "I will give you a second transcript, because I had two calls with the president of Ukraine."
Trump said the second transcript would probably be released on Tuesday.
Meanwhile, Republicans asked that former Vice President Joe Biden's son and the whistleblower whose complaint triggered the impeachment inquiry into President Trump be called to testify in public hearings that begin next week.
Democrats who control the US House of Representatives, however, likely will reject appearances by Hunter Biden and the unidentified whistleblower in the hearings due to open on Wednesday.
Devin Nunes, the top Republican on the House Intelligence Committee, included the pair in a list of proposed witnesses that he sent in a letter to the panel's Democratic chairman, Adam Schiff, published on multiple news websites.
In the letter, Nunes said the Democrats were pursuing a "sham impeachment process" that has mistreated Trump. Nunes also accused Schiff of fabricating evidence in order to cast "in a sinister light" the telephone call at the inquiry's heart.
Trump used the July 25 call - a rough transcript of which was released by the White House - to press Ukrainian President Volodymr Zelenskiy to investigate the Bidens.
Joe Biden is a leading candidate for the Democratic nomination to oppose Trump's bid for re-election next year. While he served as vice president, his son was on the board of Burisma, a Ukrainian energy firm.
The whistleblower complaint alleged that Trump used the call to seek foreign help for personal political gain, a charge broadly substantiated by the testimonies of current and former US officials in three weeks of closed hearings.
Trump and his Republican allies deny there was any wrongdoing.
Should the House impeach Trump, the Republican-controlled Senate would conduct a trial that could see him removed from office.
Nunes said he also wants testimony from Devon Archer, a businessman who served on the Burisma board with Hunter Biden, as the pair could "assist the American public in understanding the nature and extent of Ukraine's pervasive corruption".
Trump and his personal lawyer, Rudy Giuliani, have led accusations - without giving any evidence - that Joe Biden sought the dismissal of a Ukrainian prosecutor to block a corruption probe of Burisma.
In asking for the whistleblower, Nunes said that Trump "should be afforded an opportunity to confront his accusers."
Schiff likely will reject the requests for Hunter Biden, Archer and several other proposed witnesses because their testimonies - as described in Nunes' letter - appear to fall outside guidelines set by the Democrats.
He also has said there is no need to hear from the whistleblower because other witnesses broadly have substantiated the complaint.
The whistleblower alleged that Trump sought investigations into the Bidens in return for granting Zelenskiy an Oval Office visit and allowing the delivery of nearly $400mn in security aid needed by Ukraine to defend against Russia-backed separatists.