Trump earlier in the day confirmed he told staff to freeze nearly $400 million in aid to Ukraine just ahead of the phone call with Zelenskiy in which he allegedly pressured the Ukrainian leader to investigate former U.S. Vice President Biden and his son Hunter, who previously had business dealings in Ukraine.
While Pelosi's announcement adds weight to the work being done on the oversight committees, the next steps are likely to resemble the past several months of hearings and legal battles - except with the possibility of actual impeachment votes. House Democrats had considered, but never moved ahead with, pursuing articles of impeachment over Mr Trump's actions relating to Russian interference in the 2016 U.S. election aimed at boosting his candidacy.
"Now is the time to act", said Lewis, in an address to the House.
During the call, Trump told President Volodymyr Zelenskiy of Ukraine that he should be in touch with both Barr and the president's personal lawyer Rudy Giuliani, according to the transcript released by the White House on Wednesday.
But he denied claims he withheld almost $400 million in United States aid to Ukraine as leverage to get President Zelenskiy to launch a probe that would damage Mr Biden, who leads opinion polls in the Democratic race to face Mr Trump in the November 2020 election. Trump has denied that charge, but acknowledged he blocked the funds, later released.
House Democrats announced a formal impeachment inquiry Tuesday based on their suspicions that Mr. Trump tried to pressure the Ukrainian leader into investigating the Bidens by withholding $391 million in military aid last summer. He said that would be a tragedy of Trump's "own making".
Mr. Trump said the U.S.is helping Ukraine "much more than the European countries are doing, and they should be helping you more than they are".
Biden said Tuesday, before Pelosi's announcement, that if Trump doesn't co-operate with lawmakers' demands for documents and testimony in its investigations the president "will leave Congress. with no choice but to initiate impeachment".
On Tuesday evening, Pelosi announced that multiple House committees are now moving forward with an impeachment inquiry.
The official spoke on condition of anonymity in order to discuss internal investigative deliberations.
Trump has sought to implicate Biden and his son in the kind of corruption that has long plagued Ukraine.
Mr Shokin's office had opened an investigation into Burisma, a natural gas company on which Hunter Biden was a board member. There is no evidence of wrongdoing by either Joe or Hunter Biden.
But details of Trump's dealings with Ukraine prompted Democrats to quickly shift course.
The US Senate voted unanimously on Tuesday, with no objections from Trump's fellow Republicans, for a resolution calling for the whistleblower's report to be sent to Congress.
House Intelligence Committee Chairman Adam Schiff said his panel was communicating with an attorney representing the whistleblower and that the individual would like to testify this week.