WASHINGTON (Reuters) - A key Republican lawmaker said on Wednesday he did not believe the Obama administration wiretapped Trump Tower during the 2016 election campaign, adding to pressure on FBI Director James Comey to provide evidence supporting or debunking Republican President Donald Trump’s claim.

“We don’t have any evidence that that took place,” House of Representatives Intelligence Committee Chairman Devin Nunes told a news conference. “I don’t think there was an actual tap of Trump Tower.”

Trump made the claim on Twitter on March 4 without providing evidence. Nunes’ congressional committee is one of at least four that have added the startling accusation to investigations of possible Russian meddling in the election campaign and Russian ties to Trump and his associates.

James Clapper, the director of national intelligence under Obama, has said he knew of no warrant to wiretap Trump Tower.

Nunes said if Trump’s tweets were taken literally, then “clearly the president was wrong.”

With his statements, Nunes, who served on Trump’s transition team, joined other lawmakers, including some of his fellow Republicans, who have been skeptical about the president’s claim, and frustrated with what they see as federal law enforcement’s failure to provide them with information.

The top Democrat on the House intelligence panel, Adam Schiff, said at the news conference with Nunes that Comey would be asked about wiretap evidence at a rare public hearing on Monday. “It deeply concerns me that the president would make such an accusation without basis,” Schiff said.

U.S. intelligence agencies have concluded that Russia conducted cyber attacks on Democrats in an effort to influence the 2016 U.S. election on Trump’s behalf. Russia has denied this.

At the same time, Trump has been dogged by allegations that his associates had ties to Russian officials. Trump fired his national security adviser, Michael Flynn, last month after he failed to disclose contacts with Russia’s ambassador before Trump took office on Jan. 20.

House Select Committee on Intelligence Chairman Rep. Devin Nunes (R-CA) and Ranking Member Rep. Adam Schiff (D-CA) speak with the media about the ongoing Russia investigation on Capitol Hill in Washington, D.C., U.S. March 15, 2017. REUTERS/Aaron P. Bernstein

Trump seemed to back away from his accusation of wiretapping in a Fox News interview on Wednesday, saying “wiretap covers a lot of different things.”

Without providing details, the president added, “I think you’re going to find some very interesting items coming to the forefront over the next two weeks,” according to excerpts of the interview, which will air later on Wednesday.

Schiff and Nunes said they sent a letter asking Comey, Rogers and CIA Director Mike Pompeo to provide by Friday information on leaks of classified information, including names of any Americans that might have been gathered.

Schiff said he expected the Federal Bureau of Investigation to cooperate. The committee leaders said they were prepared to issue subpoenas if they did not.

In Richmond, Virginia, Attorney General Jeff Sessions told reporters that he never gave Trump any reason to believe he was wiretapped by the previous administration, according to a transcript provided by CBS News.

While White House spokesman Sean Spicer told reporters Trump “feels very comfortable” that information existed regarding surveillance conducted during 2016, a number of Trump’s fellow Republicans in Congress remained unconvinced.

Spicer told reporters traveling on Air Force One on Wednesday that Trump had not meant wiretaps specifically. “He was very clear that he used the word ‘wiretap’ generally, he put it in quotes to mean that it counts for surveillance and all types of activity of that sort,” Spicer said.

Republican Senator Lindsey Graham said he had no reason to believe a judge ever issued a warrant, which would have reflected there was probable cause that the Trump campaign was colluding with the Russians.

If it is not true, he said, the FBI should confirm that.

Graham and Democratic Senator Sheldon Whitehouse, the chairman and ranking member of the Senate Judiciary Committee’s subcommittee on crime and terrorism, asked Comey two weeks ago to provide information on Russian activities and the wiretapping by Wednesday.

Graham said on Wednesday that the FBI had responded that it would provide an answer to him and Whitehouse at a future classified briefing.

“The bottom line is a lot of Americans are wondering what’s going on here,” Graham said at a subcommittee hearing, titled “The Modus Operandi and Toolbox of Russia and Other Autocracies for Undermining Democracies Throughout the World.”

Whitehouse said he would prefer an unclassified briefing.

Comey met on Wednesday with the Judiciary Committee chairman, Chuck Grassley, and its top Democrat, Dianne Feinstein. A law enforcement official said the meeting was an opportunity for the senators to ask Comey about subjects that concern them, expected to center on FBI investigations of Trump and associates’ Russia contacts, as well as the wiretap claim.