U.S. President Donald Trump's claim that his predecessor, former President Barack Obama, wiretapped him in the weeks before last November's election is unfounded, the top leaders of the U.S. House of Representatives Intelligence Committee said Wednesday.
"We don't have any evidence that took place," Republican Congressman Devin Nunes, the panel's chairman, said. "I don't think there was a tapping of Trump Tower," the president's skyscraper headquarters in New York.
Congressman Adam Schiff, the committee's top Democrat, agreed. "To date, I see no evidence (of Obama-ordered wiretapping), no basis for that whatsoever," he said.
WATCH: Nunez says no evidence of wiretapping
WATCH: Schiff deeply concerned about Trump allegations
Awaiting info from Justice Dept.
Nunes and Schiff said they are waiting for information from the country's Department of Justice by next Monday about whether the agency knows of any court-ordered wiretaps of Trump, but said they had learned of no such bugging so far in their investigation.
The congressional probe was requested by the White House after Trump made the explosive wiretapping allegation in a March 4 Twitter comment.
The House Intelligence Committee is also looking at links between Trump campaign aides and Russian officials during the billionaire real estate mogul's long run for the White House and in the weeks after he won the election before assuming power January 20.
Nunes said that James Comey, director of the Federal Bureau of Investigation, the country's top law enforcement agency, would testify next Monday before the intelligence committee about the wiretapping allegation and the agency's investigation of Russian meddling in the election aimed at helping Trump win.
He said the panel expects to learn by Friday from U.S. investigators of any names of Trump aides who talked with Russian officials beyond the one known such contact, conversations between Trump's ousted national security adviser, retired Army general Michael Flynn, and the Russian ambassador to Washington.
Trump dismissed Flynn after he lied to Vice President Mike Pence about his contacts with the ambassador, Sergey Kislyak.
Trump first made the allegation March 4, saying, "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory."
But the president since then has provided no evidence for his claim and dodged reporters' repeated questions about the allegation.
White House spokesman Sean Spicer has sought this week to walk back Trump's contention, saying that the wire tapping allegation was meant to refer to a broader allegation of surveillance of the Trump campaign at its skyscraper headquarters in New York and not wiretapping specifically, even though that is what the president alleged.
Yet Spicer said Tuesday that Trump is "very confident" that in the end he will be vindicated about the claim.
Schiff assailed the "irresponsibility of the president and his spokesman" in making the wiretapping claim.
WATCH: Schiff on Trump's unfounded accusation of Obama
Meanwhile, a key U.S. senator, Lindsey Graham of South Carolina, says he is determined to find out whether the wiretapping claim is true.
Graham, who lost last year's Republican presidential nomination to Trump, told CNN on Wednesday, "I'm going to get to the bottom of this. Congress is going to flex its muscle."
He vowed, if need be, to subpoena the country's top law enforcement agency, the Federal Bureau of Investigation, to determine whether any U.S. judge issued a secret wiretapping edict that the FBI carried out.
Graham, voicing his doubts about Trump's wiretapping claim, has sought answers from FBI Director James Comey about the president's allegation. But the South Carolina lawmaker said that so far Comey has not disclosed any information about the purported wiretap or whether the FBI is conducting a criminal investigation of links between Trump campaign aides and Russian officials in the months before the election and after Trump won.
Graham is conducting a hearing later Wednesday on Russian interference in the election, but said that Comey would not be among the witnesses. Comey, however, is set to brief a group of senators.
The U.S. intelligence community concluded last year that Moscow interfered in the election, with Russian President Vladimir Putin ordering the hacking of the computer of John Podesta, the campaign chief for Democrat Hillary Clinton, the former U.S. secretary of state Trump defeated in the election.
Subsequently, the anti-secrecy group WikiLeaks released thousands of Podesta's emails in the weeks before the election showing embarrassing behind-the-scenes efforts by Democratic operatives to help Clinton win the party's presidential nomination.
"I don't have political hate with the president," the senator said, adding he has had recent pleasant conversations with Trump on other issues.
But Graham said the Trump wiretap allegation is "something very, very serious" and needs to be determined one way or another.