House intelligence committee Chairman Devin Nunes went to the White House on Tuesday to meet with the source who provided him documents showing that members of President Donald Trump's transition team, and perhaps Trump himself, had been swept up in incidental collection during regular surveillance of foreign operatives.

"Chairman Nunes met with his source at the White House grounds in order to have proximity to a secure location where he could view information provided by the source," a spokesman for Nunes said in a statement Monday. "The chairman is extremely concerned by the possible improper unmasking of names of U.S. citizens, and he began looking into the issue even before President Trump tweeted his assertion that the White House had been wiretapped."

Nunes, R-Calif., said Wednesday he had obtained documents that confirmed members of Trump's transition team had been overheard by U.S. spies conducting routine monitoring. He added that he was "alarmed" that Americans' whose communications had been swept up in the surveillance had their identities "unmasked" and disseminated throughout the intelligence community.

The chairman has come under fierce criticism from his Democratic counterpart, Rep. Adam Schiff of California, and other Democrats for breaking protocol in his handling of the documents, taking the unusual step of sharing the information with the president before other members of the committee had the opportunity to view it.

Schiff, whose spokesman said Monday that he still had not yet had the opportunity to review the documents, otherwise declined to comment on the revelations that Nunes met with his source on White House grounds.

Schiff and other Democrats have questioned whether Nunes should be allowed to continue to lead the committee's investigation into Russian interference in the presidential election and allegations of possible collusion between the Kremlin and Trump's campaign.

Nunes, they said, has compromised himself and the probe by sharing related information with people under investigation, including the president. And on Friday, Schiff accused Nunes of providing cover to the White House by postponing a hearing in which former top intelligence officials were set to testify publicly this week.