US President Donald Trump has blocked the release of a classified memo by congressional Democrats attempting to rebut a Republican document he allowed to be made public that claimed FBI and Justice Department bias against him in the probe of Russia and the 2016 US election.

The White House says the Justice Department had identified portions of the memo that “would create especially significant concerns for the national security and law enforcement interests” of the country.

A week ago, Mr Trump had overruled objections from the FBI about releasing the Republican memo that took aim at current and former law enforcement officials.

The House of Representatives intelligence committee voted unanimously on Monday to release the 10-page document by the panel’s Democrats, contingent on the Republican president agreeing to reclassify it.

Mr Trump allowed the release of the Republican memo on February 2, escalating a campaign against current and former senior law enforcement officials.

Democrats said that memo mischaracterised sensitive information and was intended to discredit Special Counsel Robert Mueller’s investigation of potential collusion between Mr Trump’s 2016 campaign and Russia.

Mr Mueller is also investigating whether Mr Trump has committed obstruction of justice in trying to impede the Russia probe.

“Although the president is inclined to declassify the February 5 memorandum, because the memorandum contains numerous properly classified and especially sensitive passages, he is unable to do so at this time,” White House Counsel Don McGahn says in a letter to Devin Nunes, the Republican chairman of the House panel.

The Republican memo portrays the Russia investigation as a product of political bias at the FBI and Justice Department against Mr Trump.

Democrats last week warned Mr Trump against using the Republican memo as a pretext to fire Deputy Attorney-General Rod Rosenstein, who hired Mr Mueller and oversees the investigation, or to remove Mr Mueller himself.

The Republican memo singled out Deputy Attorney-General Rosenstein and several other officials by name, including former FBI director James Comey, who Mr Trump fired in May 2017, as the agency investigated the Russia matter.

Mr 
Mueller took over the investigation from the FBI.