Former FBI Director James Comey on Thursday expressed appreciation for the FBI standing up against "weasels and liars" as debate rages over a classified memo that purports to show political bias within the Justice Department.

"All should appreciate the FBI speaking up. I wish more of our leaders would," Comey tweeted.

The bureau has come under intense scrutiny in recent weeks as Republicans seek the release of a classified memo, compiled by GOP staff and House Intelligence Committee Chairman Devin Nunes (R-Calif.), that reportedly contains allegations of surveillance program abuses during the 2016 presidential campaign.

The FBI issued a rare public statement this week saying it had "grave concerns" about the memo, adding that some information in the document was inaccurate and misleading. FBI Director Christopher Wray reportedly reiterated those concerns directly to the White House.

The FBI Agents Association on Thursday issued a statement in support of Wray as the conflicts over the memo reached a fever pitch.

Despite concerns from top officials at the Justice Department and FBI, President Trump is expected to allow the release of the memo, with an announcement expected Friday.

Democrats have called for Nunes to be removed as House Intelligence chairman over the controversy. They have also authored a countermemo they say refutes many points in the GOP version, but Republicans on the Intelligence panel voted on party lines to reject its release.

Trump fired Comey as FBI director in May, an action that precipitated the appointment of special counsel Robert Mueller to investigate Russia's election interference.

Comey has criticized the administration with varying degrees of openness since, writing on Twitter in December that he hopes "2018 brings more ethical leadership."