WASHINGTON — Representative Devin Nunes of California, the Republican chairman of the House Intelligence Committee, met on the White House grounds with a source who showed him secret American intelligence reports a day before he revealed that President Trump or his closest associates may have been “incidentally” swept up in foreign surveillance by American spy agencies.
The meeting, confirmed by his spokesman on Monday, was quite likely to further intensify questions about what prompted Mr. Nunes to make the claim about the intelligence gathering and who gave him the information.
The spokesman for Mr. Nunes, Jack Langer, said the congressman met with his source at the White House because he needed access to a secure facility where people with security clearances can legally view classified information. But such facilities can also be found in the Capitol building, and other locations across Washington.
Democrats characterized Mr. Nunes’s announcement last week as an attempt by a congressman who was eager to do the White House’s bidding to distract from the investigation into Russian meddling in the 2016 election.
Senator Mark R. Warner of Virginia, the Democratic vice chairman of the Senate Intelligence Committee, called it “more than suspicious” that Mr. Nunes went to the White House complex, pointing out that he would “have to be escorted” while there.
“Who is he meeting with?” Mr. Warner said in an interview with NBC. “Was it a source or somebody from the administration?”
Mr. Langer did not address those concerns on Monday. In a brief statement, he said: “Chairman Nunes met with his source at the White House grounds in order to have proximity to a secure location where he could view the information provided by the source.”
He added: “The chairman is extremely concerned by the possible improper unmasking of names of U.S. citizens, and he began looking into this issue even before President Trump tweeted his assertion that Trump Tower had been wiretapped.”
Acknowledging that the incidental collection from surveillance appeared to be legal, Mr. Nunes on Wednesday said his concerns surrounded additional names that may have been improperly “unmasked.” Normally, intelligence agencies mask the identities of American citizens who are incidentally present in intercepted communications.
Representative Adam B. Schiff of California, the intelligence committee’s top Democrat, said Mr. Nunes worried that anyone viewing the distributed reports could decipher who they were discussing even though the names were masked.
Mr. Nunes repeatedly declined to offer any details about the source of what he characterized as “dozens” of classified intelligence reports, which Mr. Schiff accused him of viewing in a “dead-of-night excursion.” Mr. Nunes only said the information had come to him after the committee’s public hearing on Monday.
On Friday, Mr. Nunes declined to say whether that information had come from the White House.
“You can ask me every single name that exists on the planet, and I’m still not going to tell you who our sources are,” he told reporters.
Mr. Schiff said Sunday that neither he nor, to his knowledge, anyone on the committee other than Mr. Nunes had viewed the information. “We are all quite in the dark on this,” he said in an interview on CBS’s “Face the Nation.”
Mr. Nunes’s disclosures have sparked a crisis in the House investigation into Russian meddling in the election. Bypassing Mr. Schiff entirely, Mr. Nunes said he briefed Speaker Paul D. Ryan and then White House officials, including Mr. Trump — a decision that Democrats said called the independence of both Mr. Nunes and the entire investigation into question.
Mr. Nunes on Friday defended his decision to bypass Mr. Schiff and go to the White House, saying he felt a “duty” to tell Mr. Trump because of Democrats’ “relentless” political attacks.
“If we would have crossed paths in the hall, maybe I would have said something to him,” Mr. Nunes said in an interview. “But what I was trying to do was get to the president as quick as possible.”
“It’s about the politics of this,” he added. “And I just thought that it was more important for me to get to the president of the United States because Mr. Schiff was going to find out.”
Mr. Trump seized on the information, saying he felt “somewhat” vindicated in his wiretapping claim against former President Barack Obama — debunked by the F.B.I. director James B. Comey and Adm. Michael S. Rogers, director of the National Security Agency, as well as the heads of both the Senate and House investigations, including Mr. Nunes.