WASHINGTON -- U.S. President Donald Trump was overheard telling a Republican lawmaker he was "100 per cent" in favour of releasing a classified memo on the Russia investigation, and his chief of staff said Wednesday the document is likely to be released "pretty quick."

The four-page memo, drafted by Republicans on the House intelligence committee, has touched off a partisan brawl with Democrats and pitted GOP lawmakers against the FBI and the Justice Department. The FBI director and the deputy attorney general have told the White House releasing it could set a dangerous precedent.

For his part, Trump has supported publicly disclosing the document, even though White House officials have said he hasn't read it.

Trump made his intentions clear on Tuesday night after his State of the Union address, when he was captured by television cameras chatting to lawmakers on the House floor.

When South Carolina Rep. Jeff Duncan implored him to "release the memo," Trump said: "Oh yeah, don't worry. 100 per cent."

White House spokeswoman Sarah Huckabee Sanders told CNN Wednesday that a legal and national security review of the document was continuing. Trump had not read the memo as "as of last night prior to and immediately after the State of the Union," she said.

White House Chief of Staff John Kelly said Wednesday on Fox News Radio that he expected the memo to be released "pretty quick."

The memo arrived at the White House on Monday evening after Republicans on the House committee voted to release it. Under committee rules, the president has five days to object to its disclosure.

Republicans have said the memo reveals improper use of surveillance by the FBI and the Justice Department in the Russia investigation. Democrats have called it a "cherry-picked" group of GOP talking points that attempt to distract from the committee's own investigation into Russian meddling in the election that sent Trump to the White House.

Rep. Adam Schiff, the top-ranking Democrat on the House Intelligence Committee, said Wednesday that nothing in the memo vindicates Trump. Speaking at an event sponsored by the news site Axios, Schiff said Nunes was pushing a "misleading narrative."

House Speaker Paul Ryan supports the memo's release, saying Tuesday that it shows "there may have been malfeasance at the FBI by certain individuals." He did not provide additional details, only saying that "there are legitimate questions about whether an American's civil liberties were violated by the FISA process," a reference to the Foreign Intelligence Surveillance Act.

But Ryan said the memo shouldn't be used to undermine special counsel Robert Mueller, who is investigating Russian meddling in the 2016 election and whether Trump's campaign was involved.

The vote to release the memo was unprecedented in the committee's history. The panel usually goes out of its way to protect classified information in the interest of protecting intelligence sources and methods.

In the hours before the Monday vote, Deputy Attorney General Rod Rosenstein and FBI Director Christopher Wray warned Kelly that releasing the memo publicly could set a dangerous precedent, according to a person familiar with the conversation. Rosenstein also told Kelly the memo didn't accurately characterize the FBI's investigative practices, the person said.

The Washington Post first reported the details of the White House meeting. The FBI and the Justice Department declined comment.

The Justice Department had said in a letter last week that it would be "extraordinarily reckless" to release the memo without first giving the FBI and the department the chance to review it.

After those complaints, Wray reviewed the memo over the weekend. Rep. Trey Gowdy, R-S.C., who was with Wray when he reviewed the memo, said the FBI director did not raise any national security concerns with him. Gowdy said the memo doesn't reveal any intelligence methods but it does reveal "one source."

A senior White House official said the National Security Council is leading an interagency review of the memo. If Trump decides to release the memo, it could be made public as early as Wednesday afternoon, said the official who spoke on condition of anonymity to discuss confidential internal deliberations.

So far, the official said, the Justice Department is the only agency opposing its release.

Republicans said they are confident the release won't harm national security. Democrats have said the memo's release could compromise intelligence sources and methods. And some Republican senators have also said they don't want to release it.

Associated Press writers Eric Tucker and Zeke Miller contributed to this report