Image caption All you need to know about the Trump-Russia investigation

A Republican-drafted memo alleging FBI bias against US President Donald Trump will be released on Friday, a senior White House official says.

Mr Trump is expected to declassify the document and send it to Congress for release, according to US media.

The FBI has voiced "grave concerns" about the release of the memo, which may have redactions.

It reportedly says the FBI misled an intelligence court to obtain a warrant to spy on the Trump election campaign.

Democrats say the memo is a ruse to discredit a federal inquiry into links between President Trump's presidential campaign and Russia.

The four-page document was compiled by aides for House Intelligence Committee chairman Devin Nunes, who served on the Trump team during his White House transition.

What does the memo say?

It reportedly accuses the FBI and justice department of misleading a judge in March last year while seeking to extend a surveillance warrant against Carter Page, who was a foreign policy adviser to the 2016 Trump election campaign.

The memo is said to argue that the FBI and justice department did not tell the judge that some of their justification for the warrant relied on a much-disputed Trump-Russia dossier.

Compiled by a former British intelligence agent, that dossier was financed in part through the campaign of Democratic presidential candidate Hillary Clinton to dig up dirt on Mr Trump.

Unnamed sources told Reuters news agency the Republican memo is misleading because all the dossier excerpts used in the FBI warrant application were independently confirmed by US intelligence.

Mr Page, the former Trump adviser, testified before a congressional committee last November that he met Russian government officials during a trip to Moscow in July 2016.

Image copyright AFP Image caption Aides to Republican Devin Nunes wrote the secret memo

What are Democrats' objections?

Congressional Democratic leaders called on Thursday for Mr Nunes' immediate removal as chairman of the House Intelligence Committee.

They accuse him of seeking to undermine inquiries into whether the Trump campaign colluded with the Kremlin or obstructed US investigators.

Democrats say the White House could use the memo to justify firing justice department special counsel Robert Mueller, whose Russia investigation is overhanging the Trump presidency.

The House Intelligence Committee's top Democrat, Adam Schiff, says Republicans have also amended the memo.

Mr Schiff said the text was changed after the Republicans who control the panel voted on Monday to release the document.

The California Democrat said Mr Nunes had sent the White House a version of the memo that had been "materially altered".

But an unnamed Republican aide said the amendments were grammatical changes and "minor edits", including two tweaks requested by the FBI and by Democrats.

The aide accused Democrats of an "increasingly strange attempt to thwart publication".

Why is the Department of Justice objecting?

The Republican president's declassification of the memo could pit him against his own Department of Justice.

The agency, which oversees the FBI, has warned that the memo's release could jeopardise underlying intelligence used to draft it.

It could also damage the arrangement under which US intelligence agencies brief lawmakers on secrets, with the understanding they will not end up in the public domain.

FBI Director Christopher Wray, who was appointed by President Trump, said on Thursday he will issue a rebuttal if the document is released.

The FBI issued an unusual rebuke on Wednesday to the president and his fellow Republicans in Congress.

The law enforcement bureau voiced "grave concerns about material omissions of fact that fundamentally impact the memo's accuracy".

The president has called the Russia investigation a "witch hunt" and "hoax".