Two U.S. officials say Secretary of State Mike Pompeo was on the July 25 call between President Donald Trump and Ukraine's president that is at the center of a whistleblower complaint.
The officials spoke on condition of anonymity to discuss an internal matter.
It was the first confirmation that a Cabinet official was on the call in which Trump pressed President Volodymyr Zelenskiy to investigate Hunter Biden's membership on the board of a Ukrainian gas company.
It also increases the number of people known to have first-hand knowledge of a call that has sparked an impeachment inquiry by Congress.
Secretary of State Mike Pompeo is seen at United Nations in New York last week
News of Pompeo's involvement broke after it was learned that another associate of the president is more deeply ensnared in the ongoing impeachment inquiry.
Democrats on Monday subpoenaed Rudy Giuliani, the president's personal lawyer who was at the heart of Trump's efforts to get Ukraine to investigate political rival Joe Biden's family.
That was after one of Trump's staunchest defenders, Senate Majority Leader Mitch McConnell, said he would have 'no choice' but to consider articles of impeachment if the House approved them.
With Congress out of session for observance of the Jewish holidays, Democrats moved aggressively against Giuliani, requesting by Oct. 15 'text messages, phone records and other communications' that they referred to as possible evidence.
They also requested documents and depositions from three of his business associates.
'It's a Senate rule related to impeachment, it would take 67 votes to change, so I would have no choice but to take it up,' McConnell said on CNBC.
FILE - In this May 5, 2018, file photo, Rudy Giuliani, an attorney for President Donald Trump, speaks in Washington. Giuliani says he'd only cooperate with the House impeachment inquiry if his client agreed. Central to the investigation is the effort by Giuliani to have Ukraine conduct a corruption probe into Joe Biden and his son's dealings with a Ukrainian energy company. Trump echoed that request in a July 2019 call with Ukraine's president. The House Intelligence Committee is leading the inquiry, and Chairman Adam Schiff hasn't decided if he wants to hear from Giuliani. AP Photo/Andrew Harnik, File)
The lawmakers cited claims by Giuliani in a series of TV interviews over the past week
FILE PHOTO: U.S. President Trump's personal lawyer Rudy Giuliani has coffee with Ukrainian-American businessman Lev Parnas at the Trump International Hotel in Washington, U.S. September 20, 2019. Committees are seeking documents related to his mission to seek information from Ukraine
President Trump again Monday called his phone call with the President of Ukraine where he urged him to get in touch with Giuliani 'perfect'
Giuliani has repeatedly pushed unsubstantiated claims that Joe Biden pushed Ukraine to fire a prosecutor to keep it from probing a company tied to his son
UP TO HERE: 'If (Trump) decides that he wants me to testify of course I'll testify – even though I think Adam Schiff is an illegitimate chairman,' Giuliani said.
'How long you're on it is a whole different matter.'
Trump took to Twitter to defend anew his phone call with Zelenskiy as 'perfect' and to unleash a series of attacks, most strikingly against House intelligence committee Chairman Adam Schiff.
The Democrat, he suggested, ought to be tried for a capital offense for launching into a paraphrase of Trump during a congressional hearing last week.
'Rep. Adam Schiff illegally made up a FAKE & terrible statement, pretended it to be mine as the most important part of my call to the Ukrainian President, and read it aloud to Congress and the American people,' the president wrote.
'It bore NO relationship to what I said on the call. Arrest for Treason?'
Trump tweeted repeatedly through the day but was, for the most part, a lonely voice as the White House lacked an organization or process to defend him.
Senior staffers, including acting chief of staff Mick Mulvaney and White House counsel Pat Cipollone, were to present Trump this week with options on setting up the West Wing's response to impeachment,