WASHINGTON - Former FBI director James Comey was so appalled by President Donald Trump's request to drop an investigation into ties between former White House national security adviser Michael Flynn and Russia that he wanted to document it, CNN reported, citing a source.
He shared the memo with FBI senior officials, the source added.
"You realise something momentous has happened and memories fade so he wanted to memorialise it at the earliest time," the source said according to CNN.
The expectation is that the memos will be subpoenaed, according to a source familiar with the matter. The source says Mr Comey wants to tell his story either in testimony to Congress, or in an interview or speech.
A second source told CNN's Jake Tapper that Mr Comey wants to testify and do so publicly.
The Comey memo, first reported by the New York Times on Tuesday (May 16), caused alarm on Capitol Hill and raised questions about whether Mr Trump tried to interfere with a federal investigation.
Mr Comey wrote the memo after he met in the Oval Office with Mr Trump, the day after the Republican president fired Mr Flynn on Feb 14 for misleading Vice-President Mike Pence about the extent of his conversations last year with Russia's ambassador Sergei Kislyak.
"I hope you can let this go," Mr Trump told Mr Comey, according to a source familiar with the contents of the memo.
The explosive new development followed a week of tumult at the White House after Mr Trump fired Mr Comey and then discussed sensitive national security information about Islamic State with Russian Foreign Minister Sergei Lavrov.
The White House quickly denied the report, saying in a statement it was "not a truthful or accurate portrayal of the conversation between the president and Mr Comey".
Lawmakers called for more information, however. In a letter to acting FBI director Andrew McCabe, the Senate Oversight Committee demanded that all memos and other documents or recordings relating to communications between Mr Trump and Mr Comey be turned over by May 24, Reuters reported.
"If true, these memoranda raise questions as to whether the president attempted to influence or impede the FBI's investigation as it relates to Lieutenant-General Flynn," wrote committee chairman Jason Chaffetz, a Republican.