The Republican head of a congressional inquiry into alleged Russian meddling in the 2016 US presidential election said he would temporarily step aside from the probe because he is under investigation for disclosing classified information.
Devin Nunes, chairman of the House of Representatives Permanent Select Committee on Intelligence and an ally of Republican President Donald Trump, described charges that he made unauthorised disclosures of classified information as "entirely false and politically motivated".
The surprise disclosure that Mr Nunes was under investigation added new uncertainty to the wider Russia probe his committee is carrying out.
The investigation is one of several in Congress examining whether Russia tried to influence the election in Trump's favour, mostly by hacking Democratic operatives' emails and releasing embarrassing information. Russia denies the allegations.
The House Ethics Committee issued a rare statement saying it would investigate allegations Mr Nunes may have made unauthorised disclosures of classified information "in violation of House Rules, law, regulations, or other standards of conduct".
Mr Nunes said in a statement that he had decided to step aside from the Russia investigation to fight the allegations and wanted "to expedite the dismissal of these false claims".
Representative Mike Conaway, the most senior Republican on the intelligence committee, will be the new leader of the probe.
The top Democrat on the panel, Representative Adam Schiff, said Mr Nunes' decision to step aside from the probe was made in "the best interests of the committee, and I respect that decision."
Democrats have criticised Mr Nunes, a member of Mr Trump's transition team, for his handling of the Russia investigation after he received information at the White House, held a news conference about it and briefed Mr Trump on it, all before sharing it with other members of his committee.
The ethics investigation stems from whether Mr Nunes disclosed classified information while publicly discussing the contents of foreign intelligence reports.