The Republican chairman is stepping aside from leading a congressional investigation of Russian interference in last year's U.S. presidential election, citing ethics complaints that he mishandled classified information.

The decision by Rep. Devin Nunes of California comes amid partisan turmoil on the House intelligence committee. Democrats have alleged that Nunes, who was on President Donald Trump's transition team, is too close to the White House and cannot lead an impartial inquiry. In an extraordinary step, the usually-quiet House Ethics Committee said that it is investigating whether Nunes improperly disclosed classified information. President Donald Trump said Nunes is "a very honourable guy."

Nunes blamed "left-wing activist groups" for filing accusations against him with the Office of Congressional Ethics.

Story continues below advertisement

"The charges are entirely false and politically motivated and are being levelled 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.

Nunes' move could be seen as a win for Democrats whose cries for an independent panel to investigate Russia's possible ties with the Trump campaign have grown. They have pointed in particular to two Nunes trips to the White House — one announced, one not — as evidence that his loyalty to Trump outweighs his commitment to leading a bipartisan investigation.

By all accounts, the intelligence committee's growing partisanship has become a distraction from its underlying investigations.

The top Democrat on the committee, Adam Schiff of California, said he appreciated Nunes' decision to step aside from the Russia investigation.

"There was a cloud hanging over us after the White House incident," Schiff told The Associated Press on Thursday. While Schiff said the panel's investigation is back on track, the Republicans had not signed off on rescheduling a public hearing with former Obama administration officials. Schiff said it was important that the public hear testimony from former acting Attorney General Sally Yates about why Trump's first national security adviser was fired. Nunes cancelled the hearing.

As the majority party in the House, Republicans will keep the committee chairmanship. GOP Rep. Mike Conaway of Texas, with help from Rep. Trey Gowdy of South Carolina and Rep. Tom Rooney of Florida, will temporarily take charge of the investigation, said Speaker Paul Ryan.

Trump told reporters aboard Air Force One on Thursday that he doesn't know Conaway, but he heard he was well-respected. "High quality," Trump said.

Story continues below advertisement

Schiff said Conaway does not have the same history with the White House that Nunes does.

Two watchdog groups, Democracy 21 and Citizens for Responsibility and Ethics in Washington, or CREW, had asked the House Ethics Committee to investigate whether Nunes disclosed classified information he learned from intelligence reports.

In a statement, CREW spokesman Jordan Libowitz said the group believes that Nunes' potential violation of House ethics rules "is so grave that it needs to be investigated right away."

Nunes last month disclosed that Trump associates' communications had been swept up by U.S. spy agencies and, he suggested, mishandled by Obama administration officials.

The announcement was striking, as it is unusual for a member of the committee to publicly discuss the existence of what would be classified intelligence reports.

Nunes later acknowledged that the material had been shared by a secret source on the White House grounds, raising fresh questions about his co-ordination with the White House. Trump seized on the information as evidence backing up his unfounded claim that President Barack Obama wiretapped the phones at his New York skyscraper.

Story continues below advertisement

Schiff later saw the same material, but refused to publicly discuss what he learned. He said Thursday he understood the material was now to be shared with other intelligence committee members.

Republican Speaker Ryan said he supported Nunes' decision to step aside.

"It is clear that this process would be a distraction for the House intelligence committee's investigation into Russian interference in our election," Ryan said.

A Republican aide said Nunes met with Ryan on Wednesday night to discuss stepping aside from the Russia probe. That's when Ryan learned of the House ethics probe, according to the aide, who spoke on condition of anonymity to discuss private conversations.

Nunes said in his statement, "I will continue to fulfil 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 Ethics Committee investigation of Nunes' actions will be led by Republican Chairwoman Susan Brooks of Indiana and Democrat Ted Deutch of Florida.

Story continues below advertisement

Conaway's ascendance immediately drew attention to his statement earlier this year expressing skepticism about the subject of the investigation.

In January, Conaway compared Russia's interference in the 2016 election to the Democrats' employing Mexican entertainers to help turn out the Latino vote.

"Those are foreign actors, foreign people, influencing the vote in Nevada," Conaway told the Dallas Morning News. "You don't hear the Democrats screaming and saying one word about that."

During the intelligence committee's first hearing on the Russia probe last month, his questions were focused on how intelligence agencies prove who is behind a hack and what a foreign leader's "intent" is.

All 17 intelligence agencies have agreed that Russia was behind the hack of Democratic email systems and tried to influence the 2016 election to benefit Trump.