A second person has come forward with first-hand information about US President Donald Trump's alleged attempts to press Ukraine for personal political gain.
The whistleblower's lawyer Mark Zaid said the person was an intelligence official who "has first-hand knowledge of some of [the] allegations outlined in the original complaint", ABC News reported on Sunday.
The informer has been interviewed by the head of the intelligence community's internal watchdog.
Mr Zaid retweeted ABC's reports on the development. He was expected to appear on ABC's This Week.
The original whistleblower complained that Mr Trump was "using the power of his office to solicit interference from a foreign country" in the 2020 US election.
Mr Trump and his supporters have rejected the accusations that he did anything improper.
"I can confirm that my firm and my team represent multiple whistleblowers in connection to the underlying August 12, 2019 disclosure to the intelligence community inspector general," tweeted Andrew Bakaj, managing partner at Mr Zaid's firm Compass Rose Legal Group.
The existence of the second whistleblower followed discontent within Mr Trump's Republican Party after he urged Beijing on Friday to investigate former vice president Joe Biden's son, who had business dealings in China.
Republican senators Mitt Romney, Ben Sasse and Susan Collins all expressed concerns about Mr Trump contacting foreign countries to help him in his 2020 re-election bid.
The whistleblower complaint prompted House of Representatives Speaker Nancy Pelosi to launch impeachment proceedings on September 24 against Mr Trump, saying his actions jeopardised US election integrity and threatened national security.
The Trump administration complained on Saturday of harassment by Democratic politicians who issued subpoenas for documents regarding the president's alleged pressuring of Ukraine for political favours.