Two leading Republican senators have joined Democrats in questioning the objectivity of the chairman of House of Representatives intelligence committee in its investigation of possible Russian ties to US President Donald Trump's election campaign.
Senators John McCain and Lindsey Graham stopped short of calling on the chairman, Representative Devin Nunes, to recuse himself but their Democratic counterparts had already done so on Monday.
The outcry over Nunes' actions since FBI Director James Comey confirmed the FBI was investigating possible ties between Russia and the Trump campaign could add momentum to calls for an independent commission to investigate the matter.
"I think he put his objectivity in question, at the very least," Graham said on NBC's "Today" show.
Nunes told reporters on Tuesday morning the investigation was moving forward.
The spectre of possible Russian influence on the presidential election in Trump's favour has cast a shadow over the Republican president, who took office on January 20.
Attorney General Jeff Sessions, a Trump campaign adviser, has recused himself from FBI probes involving Trump.
This week, the Senate Intelligence Committee, which is also investigating Russia's role in the election, said it wanted to question Trump's son-in-law and adviser, Jared Kushner, about meetings he held with the ambassador and a Russian banker in December.
Nunes acknowledged visiting the White House the night before he announced that he had information that some Trump associates may have been snared in incidental intelligence collection before Trump took office on January 20.
Critics said the announcement was an effort to justify Trump's unfounded accusations on Twitter on March 4 that his Democratic predecessor, Barack Obama, had directed surveillance on Trump Tower during the campaign.
"If he's not willing to tell the Democrats and Republicans on the committee who he met with and what he was told, then I think he's lost his ability to lead," Graham said.
Nunes compromised his credibility by not sharing the new information, or its source, with committee colleagues, McCain said.
"There needs to be a lot of explaining to do. I've been around for quite a while and I never heard of any such thing," McCain said.
