"Several left-wing activist groups have filed accusations against me with the Office of Congressional Ethics. The charges are entirely false and politically motivated and are being leveled just as the American people are beginning to learn the truth about the improper unmasking of the identities of U.S. citizens and other abuses of power," Nunes said in a statement released this morning.
But he said today that Republican Rep. Mike Conaway of Texas, with assistance from GOP Reps. Trey Gowdy of South Carolina and Tom Rooney of Florida, will "temporarily" lead the committee's Russia probe while the House Ethics Committee looks into the matter.
"I will continue to fulfill all my other responsibilities as committee chairman, and I am requesting to speak to the Ethics Committee at the earliest possible opportunity in order to expedite the dismissal of these false claims," the statement concluded.
Leaving Capitol Hill Thursday, Nunes declined to elaborate further, referring reporters back to his statement as he got into a car outside the Capitol.
The House Ethics Committee announced today that it is investigating Nunes' actions after "allegations of unauthorized disclosures of classified information," noting that the investigation "does not itself indicate that any violation has occurred."
The committee cited "public allegations" against Nunes in its statement. A handful of liberal watchdogs like Moveon.org, Democracy 21 and Citizens for Responsible Ethics in Washington have filed complaints against Nunes with the nonpartisan Office of Congressional Ethics, accusing Nunes of disclosing classified information in public statements about Trump associates getting caught in surveillance of foreign targets.
According to the committee rules, the decision to open the probe was made jointly by Chairwoman Susan Brooks, R-Indiana, and ranking member Ted Deutch, D-Florida, and did not require a full panel vote.
The White House declined to comment on Nunes' decision to step aside. "I'm not going to comment on decisions that the House makes on its committee chairman or their activities that's up to them," White House press secretary Sean Spicer told ABC News today.
House Speaker Paul Ryan, who said March 28 that he did not think Nunes should recuse himself, defended Nunes' integrity but said he supports the decision.
"Devin Nunes has earned my trust over many years for his integrity and dedication to the critical work that the intelligence community does to keep America safe," Ryan said in a statement. "He continues to have that trust, and I know he is eager to demonstrate to the Ethics Committee that he has followed all proper guidelines and laws. In the meantime, it is clear that this process would be a distraction for the House Intelligence Committee's investigation into Russian interference in our election.
"Chairman Nunes has offered to step aside as the lead Republican on this probe, and I fully support this decision. Chairman Mike Conaway, a senior member of the committee, will now lead this investigation in the House. I am confident that he will oversee a professional investigation into Russia's actions and follow the facts wherever they lead," Ryan said.
Conaway said in a statement that he is "confident that ranking member Schiff and I will be able to work together to conduct an effective, bipartisan investigation.”
The Texas Republican said Nunes still has his "full support," and that he believes the leadership adjustment will be "temporary."
Ryan met with Nunes Wednesday night to speak about the California representative stepping aside in the investigation, according to a GOP leadership aide. Representatives on the House Intelligence Committee did not learn of the decision until a meeting Thursday.
Nunes appeared at the meeting briefly, but then left the group, at which point committee staff handed the members a copy of the statement announcing Nunes' move, according to one member in the room. Even Rep. Adam Schiff, the ranking Democrat on the committee, said he learned of the news "when everyone else got notice through the chairman's statement."
Schiff said he is looking forward to working with Nunes on other issues but said he agrees with the decision to remove himself.
"I'm sure it was a very difficult decision for him, but, as he mentioned, I do think it's in the best interest of the investigation," Schiff said today.
"This investigation is of such importance that we have to get fully back on track," he added.
Nunes was named to the executive committee of Trump's transition team on Nov. 11, 2016. During the transition phase, he advised Trump on his selections for Cabinet posts and other top jobs in the incoming administration.
Heading into a two-week recess, members of the House Intelligence Committee hope Nunes' recusal will put the committee on stronger footing with its investigation. The panel is expected to begin interviewing witnesses when members return from Easter recess.
"We were moving along but I do think this will have the effect of at least temporarily eliminating questions of impartiality," Rep. Jim Himes, D-Connecticut, a member of the panel, said in an interview with ABC News.
ABC News' John Parkinson and Cecilia Vega contributed to this report.