WASHINGTON — With threats of subpoenas and efforts to block a top Justice nominee, congressional leaders are ramping up pressure on the Justice Department and FBI to acknowledge whether there is any information to support President Trump's widely disputed claim that the Obama administration wiretapped his New York offices in advance of the November election.

The chairman of the House Intelligence Committee told reporters Wednesday he has seen no evidence to support the claim.

“We don't have any evidence that that took place,” Rep. Devin Nunes, R-Calif., said during a news conference at the Capitol. “I don't think there was an actual tap of Trump Tower.”

Nunes said it was obvious that President Obama personally did not personally install listening devices the building where Trump has offices and an apartment, so he said the committee has had to try to determine what the president did mean if his tweet could not be taken literally.

“If the White House or the president want to come out and clarify his statements more, it would probably, probably be helpful,” Nunes said.

Sen. Lindsey Graham, R-S.C., a senior member of the Judiciary Committee, indicated earlier Wednesday that he has bipartisan support to seek subpoenas if FBI Director James Comey does not respond to Trump's wiretap claims and outline the status of the bureau's ongoing investigation into communications between Trump associates and Russian government officials.

"I think the entire country needs to know if there's something there,'' Graham said on NBC's Today show. "Congress is going to flex its muscle.''

If the request is not satisfied, Graham said there is Judiciary Committee support for issuing subpoenas to compel the information and to block the pending nomination of Rod Rosenstein, who is awaiting confirmation as the deputy attorney general.

Rosenstein's position is especially crucial since Attorney General Jeff Sessions recused himself from overseeing the federal Russia inquiry after it was disclosed that the former Alabama senator had met twice with the Russian ambassador to the United States during the course of the general election campaign. Sessions did not disclose the meetings during his January confirmation hearings.

Earlier this week, the Justice Department, facing a separate deadline from the House Intelligence Committee to turn over information that might support Trump's wiretap claims, asked for additional time to determine whether any information exists.

Nunes also said Wednesday he was demanding more answers from the intelligence community about efforts they make to prevent the release of the names of Americans who are caught during surveillance of foreign officials.

He and Rep. Adam Schiff, a California Democrat who is the ranking member of the panel, released a letter seeking answers about “unmasked” American identities by Friday. Nunes and Schiff said the committee would use its subpoena power if it does not get answers.

Comey and Adm. Michael Rogers, director of the National Security Agency, will testify at a public hearing the Intelligence Committee will hold Monday, Nunes said. Another hearing will be held March 28 to hear from other witnesses.

Schiff said Comey would be asked publicly whether he has seen any evidence that substantiates Trump’s claim.

“It deeply concerns me that the president would make such an accusation without basis,” Schiff said.

He said it could be Trump was just reacting to something he saw on television, and the White House reaction has evolved over time.

“You can't level an accusation of that type without retracting it or explaining just why it was done,” he said. “I think there are, from a national security perspective, great concerns if the president is willing to state things like that without any basis, because the country needs to be able to rely on him, particularly if we have a crisis.

Shortly after Trump issued his wiretap claims in a series of tweets, Comey asked that Justice officials refute the president's allegations. The Justice Department has not acted on that request. Separately, former director of national intelligence James Clapper has publicly denied that such surveillance of Trump Tower existed.