(Reuters)

FBI Director James B. Comey huddled with top lawmakers Thursday as pressure grows on the Justice Department to either substantiate or denounce President Trump’s accusation that the Obama administration tapped his phones during the presidential campaign.

Intelligence Committee and party leaders in the “Gang of Eight” — senior congressional leaders who receive the highest-level briefing — held meetings in both chambers of Congress. Members emerging from the meeting, including Senate Minority Leader Charles E. Schumer (D-N.Y.) and Mark R. Warner (D-Va.), were tight-lipped about the substance of the conversation.

The meetings come as lawmakers sent letters to Comey and acting deputy attorney general Dana Boente demanding a full accounting of any wiretapping applications, orders or warrants issued in an effort to conduct surveillance on Trump or his surrogates and associates during the campaign.

The president charged in tweets Saturday morning that President Barack Obama ordered the wiretapping of his New York offices in the fall, presumably in an attempt to gain more information about Russia’s meddling in the U.S. election. The House Intelligence Committee is probing that charge, as well as allegations that Trump associates have links to Russia — Trump has also asked that the wiretapping charge be included in the probe. The FBI is investigating Russia’s suspected intervention in the election, as well as the alleged links of Trump’s team to Russia.

House Intelligence members may get their chance to grill Comey in a public hearing scheduled for March 20. The invitation list includes Comey, National Security Agency Director Michael S. Rogers, former acting attorney general Sally Yates, former director of national intelligence James R. Clapper Jr., former CIA director John Brennan, and two senior officers of CrowdStrike — the company that found proof Russia hacked the Democratic National Committee’s servers. No subpoenas have been issued.

FBI Director James Comey . (Brian Snyder/Reuters file photo)

Comey’s trip to Capitol Hill comes as lawmakers are divided — not always along party lines — over whether the director is keeping the Gang of Eight adequately informed about the intelligence the FBI and Justice Department have collected that could bear on the congressional investigation into alleged Trump-Russia ties.

Rep. Adam B. Schiff (D-Calif.) sent a letter dated Wednesday to Boente, who took over ultimate responsibility for much of the department’s probe after Attorney General Jeff Sessions recused himself from all matters pertaining to the Trump campaign. The letter asked for copies of any wiretapping applications, orders or warrants from 2016 relating to Trump, his surrogates, associates, family members and friends. The heads of the Senate Judiciary Committee’s crime and terrorism panel, Sens. Lindsey O. Graham (R-S.C.) and Sheldon Whitehouse (D-R.I.), also sent a letter to Boente and Comey Wednesday asking for a similar list of documents.

Few members of Congress believe the president’s allegations about the Obama-ordered wiretap, and several are demanding that the Trump administration produce evidence to substantiate the claim. The White House has refused to do so, calling on Congress to conduct an investigation into the matter.

Meanwhile, Graham and Whitehouse sent their letter to the FBI and the Justice Department Wednesday with the blessing of Judiciary Committee Chairman Charles E. Grassley (R-Iowa), he said Thursday. Grassley said that asking for those records was “a proper thing to do” as part of a hearing on Russia’s alleged involvement in the 2016 elections that Graham and Whitehouse are expected to schedule soon.

But Grassley said he is dissatisfied with Comey’s lack of response to those and other requests for relevant information

Grassley and Judiciary Committee ranking Democrat Dianne Feinstein (Calif.) called Comey on Monday, he said, in an attempt to schedule a briefing they had previously requested from him, aimed at discussing Russia’s alleged election meddling.

“We get this excuse: I’m talking to the DOJ now to get, more or less, to get clearance,” Grassley said, frustrated. “And I said . . ., ‘Did you have clearance when you talked to the Intelligence Committee last week?’ ”

“It surprised me, but here’s the bottom line: Four days later we still haven’t heard back from him,” Grassley said.

Warner and Sen. Richard Burr (R-N.C.), however, met with Comey on Thursday, and have expressed satisfaction with the level of candor and access he has been offering them to collected intelligence relevant to their investigation.

But in the House, some Intelligence Committee members are markedly unsatisfied with the access Comey has been giving them.

“We need the confidence of knowing that they’re briefing us on the most significant issues,” Schiff told reporters last week. “And at this point, I think that’s very much in question.”

Rank-and-file Intelligence Committee members have begun to make trips to CIA headquarters to review documents made available to them by the intelligence community. Those trips began earlier this week in the Senate.

Rep. Eric Swalwell (D-Calif.), a member of the Intelligence Committee, said Thursday that access for House members just recently became available. He also credited Schiff and Rep. Devin Nunes (R-Calif.) for “pushing, as far as I’ve been told” to make sure access to other information and officials is “expanded to the full membership” of the committee.