A second whistle-blower in the impeachment inquiry against US President Donald Trump has come forward, according to the lawyer representing the first one.
Mark Zaid told The Associated Press news agency in a text message on Sunday that the second whistle-blower, who also works in intelligence, has spoken to the intelligence community's internal watchdog.
The lawyer said the second person did not file a complaint with the inspector general but does have "first-hand knowledge that supported" the original whistle-blower.
Zaid represents the first whistle-blower who filed a complaint on August 12 involving a July 25 phone call Trump held with Ukraine's President Volodymyr Zelensky in which he asked him to investigate a Democratic rival, former Vice President Joe Biden.
The complaint alleged Trump was "using the power of his office to solicit interference from a foreign country" in the 2020 election.
There was no immediate comment by the White House on Sunday's reports. Trump and his supporters have rejected the accusations that he did anything improper.
But the telephone call and the whistle-blower complaint prompted House of Representatives Speaker Nancy Pelosi to launch impeachment proceedings on September 24 against Trump, saying his actions jeopardised US election integrity and threatened national security.
Al Jazeera's Shihab Rattansi, reporting from Washington, DC, said the development on Sunday did not refer to "multiple official whistle-blower complaints" but "corroboration" of the initial whistle-blower complaint, adding that it is possible that the development could mean "not much" for the impeachment inquiry.
"Things are solidified already, it would seem. The House Democrats are investigating these complaints. It would appear that most of them have already made up their mind that an impeachable offence might have occurred," he said.
"We should remember that there are different ways of looking at what happened, and the impeachable offence doesn't necessarily mean a criminal offence or something that is in statute book of law. It's a much lower standard, it's more about misdemeanours, but Congress can very much define what those actually mean," he added.
The existence of the second whistle-blower followed expressions of discontent within Trump's own Republican Party after he called on China on Friday to investigate Biden's son, who had business dealings in China.
No administration officials were scheduled to appear on the Sunday news shows, while several congressional Republicans who were interviewed came to the president's defence.
Ohio Representative Jim Jordan, one of Trump's most vocal defenders, sharply criticised the way House Democrats are handling the impeachment inquiry.
A Democrat on the House Intelligence Committee, Florida Representative Val Demings, said she believes the original whistle-blower is a "patriot" who stepped forward to report wrongdoing despite the potential career risk.
"The reporting that a second whistle-blower has come forward or is about to come forward, I believe again would be someone who sees wrongdoing, hears wrongdoing and wants to do something about it," Demings said.
The latest development in the politically-explosive inquiry comes after Secretary of State Mike Pompeo said the State Department intends to follow the law as House Democrats press their demands for information from the administration.
Pompeo said the department sent a letter to Congress on Friday night as its initial response to the document request and added: "We'll obviously do all the things that we're required to do by law."
He is allowing Democrats to interview a series of department witnesses this coming week. Among them is Gordon Sondland, the US ambassador to the European Union, another key figure in the investigation.
The administration has struggled to come up with a unified response to the quickly progressing investigation.
Democrats have warned that defying their demands will in itself be considered "evidence of obstruction" and a potentially impeachable offence.