WASHINGTON - The whistleblower whose complaint has led to an impeachment inquiry against President Donald Trump is a CIA officer, US media report.
The unnamed officer once worked at the White House, several US outlets said.
The whistleblower says senior White House officials tried to "lock down" all details of a phone call between Mr Trump and the Ukrainian president.
Mr Trump demanded to know who gave information to the whistleblower, saying the source was "close to a spy".
In the call on 25 July, Mr Trump pushed Volodymyr Zelensky to investigate his leading Democratic political rival, Joe Biden.
The complaint, released on Thursday, says the call transcript was not stored in the usual computer system. Instead it was stored in a separate system used for classified
A rough transcript of the conversation, released by the White House this week, shows that the president urged his newly elected Ukrainian counterpart to investigate
discredited corruption allegations against Mr Biden and his son Hunter.
"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that," he told Mr Zelensky.
Democrats accuse Mr Trump of illegally seeking foreign help in the hope of smearing Mr Biden - who is seeking the Democratic nomination for the 2020 presidential
He also called on the Ukrainian leader to talk to US Attorney General William Barr and Mr Trump's lawyer Rudy Giuliani about investigating Hunter Biden's past
business dealings in Ukraine.
Mr Trump is also accused of using military aid to Ukraine as a bargaining tool. The package - which has since been released - had been appropriated by Congress to
support the interests of US interests in a friendly country.
Mr Trump, a Republican, denies any wrongdoing and has dismissed the impeachment proceedings as a "hoax" and "another witch-hunt".
He acknowledged that he had personally blocked nearly $400m (£322m) in military aid to Ukraine days before he spoke to Mr Zelensky, but denied that it was to
pressure the Ukrainian leader into investigating Mr Biden.
Few details are known. A lawyer for the whistleblower warned that trying to identify the person could place them "in harm's way".
The New York Times, Washington Post, and Reuters news agency identified the whistleblower as a CIA officer.
Meanwhile, an audio recording has emerged in which Mr Trump demands to know who provided information to the whistleblower - and describes them as "close to a