The whistleblower, who divulged that President Donald Trump had sought foreign help for his re-election and that the White House sought to cover it up, is a CIA official who was detailed to work at the White House at one point.
Quoting three people familiar with his identity, The Irish Times reported that the whistleblower's complaint made public on Thursday suggested that he was an analyst by training and demonstrated a sophisticated understanding of Ukrainian politics and some knowledge of the law.
However, little else is known about him.
Lawyers for the whistleblower refused to confirm that he worked for the CIA and said that publishing information about him was dangerous.
"Any decision to report any perceived identifying information of the whistleblower is deeply concerning and reckless, as it can place the individual in harm's way," said Andrew Bakaj, his lead counsel.
"The whistleblower has a right to anonymity," the counsel added.
A CIA spokesman declined to comment.
Trump took aim at the whistleblower's credibility on Thursday, attempting to dismiss his revelations because they were second-hand. He also obliquely threatened the whistleblower or his sources with punishment.
"I want to know who's the person who gave the whistleblower the information because that's close to a spy," Trump told staff members from the US Mission to the United Nations before an event there.
He said, "You know what we used to do in the old days when we were smart with spies and treason, right?" adding, "We used to handle it a little differently than we do now."
During a telephonic conversation with his Ukrainian counterpart Volodymyr Zelenskiy, on July 15, Trump had asked him to investigate unsubstantiated allegations of corruption against former US Vice President Joe Biden and his son and other matters he saw as potentially beneficial to him politically.
Trump cajoled Zelenskiy to co-ordinate with attorney general William Barr and the president's personal lawyer Rudy Giuli, according to a reconstituted transcript of the call that the White House released on Wednesday.
Meanwhile, Zelenskiy, who was elected in April, agreed to help Trump during the call.
( With inputs from ANI )