WASHINGTON (REUTERS) - The top Republican in Congress on Tuesday (March 28) stood by Devin Nunes, the embattled head of the House of Representatives intelligence committee, who is under fire for his handling of an investigation into possible Russian ties to President Donald Trump's election campaign.

House Speaker Paul Ryan told a news conference he does not believe Nunes, a Trump ally, should remove himself from the investigation. Asked whether Nunes should step aside and if he knew the source of information that Nunes revealed last week, Ryan said, "No and no."

Democrats and some Republicans have criticized Nunes' objectivity after he announced last week that some Trump associates may have been ensnared in incidental intelligence collection before Trump took office in January.

Critics have said the disclosure was an effort to justify Trump's unfounded accusations in early March that his Democratic predecessor, Barack Obama, had directed surveillance on Trump Tower during the election campaign. Nunes acknowledged visiting the White House before making the announcement but has refused to say who he met with or who was source for his claims about the collection of incidental intelligence.

The spectre of possible Russian influence on the presidential election in Trump's favour has cast a shadow over the Republican president's first two months in office. He fired his national security adviser, Michael Flynn, last month for misrepresenting meetings with the Russian ambassador.

Nunes, who was a member of the team that ran Trump's transition to the presidency after the November 8 election, told reporters on Tuesday the Russia investigation was moving forward. Asked whether he would recuse himself, he said, "The investigation continues."

Ryan spokeswoman AshLee Strong said in an email on Tuesday,"Speaker Ryan has full confidence that Chairman Nunes is conducting a thorough, fair, and credible investigation."