Trump administration officials have tried to ’’lock down’’ all details of the US president’s phone call to Ukraine’s leader.
In the call, Donald Trump pushed Volodymyr Zelensky to investigate corruption claims involving Joe Biden’s son.
The newly released report says the transcript was not stored in the computer system normally used for such information.
Instead, it says, it was stored in a separate system used to store “classified information of an especially sensitive nature”.
Mr Biden – the leading Democratic presidential hopeful – says a rough transcript of the conversation released on Wednesday shows the president betrayed his oath of office.
Democrats opened an impeachment inquiry against the Republican president on Tuesday, accusing Mr Trump of seeking foreign help in the hope of smearing Mr Biden and of using military aid to Ukraine as a potential bargaining tool.
The report’s release comes as US lawmakers are beginning to question President Trump’s top intelligence official over the issue.
Acting national intelligence director Joseph Maguire had initially refused to share the complaint with Congress.
President Trump has dismissed the impeachment proceedings as a “hoax” and a “witch-hunt”.