WASHINGTON - Top congressional Republicans began calling Thursday for Attorney General Jeff Sessions to recuse himself from any investigation of the Trump campaign's contacts with Russia after revelations that Sessions met with the Russian ambassador to the United States while advising the Trump campaign but did not disclose those meetings during his confirmation hearing.

Ohio Republican Sen. Rob Portman said Thursday, “Jeff Sessions is a former colleague and a friend, but I think it would be best for him and for the country to recuse himself from the DOJ Russia probe.”

Rep. Jason Chaffetz, R-Utah, chairman of the House Oversight and Government Reform Committee, tweeted Thursday that "AG Sessions should clarify his testimony and recuse himself."

House Majority Leader Kevin McCarthy of California said in an appearance on MSNBC that the attorney general should recuse himself in order to maintain "the trust of the American people." But later Thursday morning, he appeared on Fox & Friends to walk back his comments. "I'm not calling on him to recuse himself," McCarthy said. He explained that he was merely repeating Sessions' position that the attorney general should recuse himself if and when that becomes appropriate.

Sessions on Thursday told NBC News "I have not met with any Russians at any time to discuss any political campaign." He also repeated his prior statements that he will recuse himself from an investigation if it becomes necessary at some point.

Sessions, who was a U.S. senator from Alabama and Trump campaign adviser when he met with the Russian ambassador, has denied discussing campaign-related matters with Russian officials.

"I never met with any Russian officials to discuss issues of the campaign," Sessions said in a statement released late Wednesday. "I have no idea what this allegation is about. It is false."

During the hearings to confirm Sessions as U. S. Attorney General Minnesota Senator Al Franken (D), in the wake of a report by CNN that the Trump campaign had engaged in contact with the Russians, asked Sessions what he would do if he learned that the reports were true.

"I'm not aware of any of those activities.... I did not have communications with the Russians, and I am unable to comment," he testified.

Leading Democrats are calling the testimony perjury, and are pressing Sessions to step down as AG. "Now, after lying under oath to Congress about his own communications with the Russians, the attorney general must resign," House Democratic Leader Nancy Pelosi said in a statement. "Sessions is not fit to serve as the top law-enforcement officer of our country and must resign. There must be an independent, bipartisan, outside commission to investigate the Trump political, personal, and financial connections to the Russians."