The chair of the U.S. House of Representatives intelligence committee said on Tuesday he had seen no evidence to support President Donald Trump's allegation he was wiretapped by then president Barack Obama during the 2016 presidential campaign.

Republican Representative Devin Nunes said that if Trump's assertion were true, the leaders of Congress and chair of its two intelligence committees, known collectively as the "Gang of Eight," should have been briefed.

"I have not seen that evidence," Nunes told a news conference. "I think the bigger question that needs to be answered is whether or not Mr. Trump or any of his associates were in fact targeted by any of the intelligence agencies or law enforcement authorities."

Trump made the accusation in tweets on Saturday, providing no evidence. An Obama spokesperson denied it.

"The president is a neophyte to politics — he's been doing this a little over a year," Nunes told reporters. "I think a lot of the things he says, I think you guys sometimes take literally."

Trump has since pressed the House and Senate intelligence committees to expand probes into allegations that Russia meddled in the U.S. election to look into his charge.

"We are supposed to be kept up to speed on any pertinent counterintelligence investigation," Nunes said. "If Trump or any other political campaign, or anybody associated with Trump, was under some type of investigation, that clearly should have risen to the Gang of Eight level."

Democrat calls accusation 'a scandal'

Adam Schiff, the top committee Democrat, also said it did not appear that the group had been appropriately briefed.

Schiff said it was "a scandal" that Trump had levied the accusation against Obama. He said the intelligence panel would address the issue and deal with it quickly.

"The president has said that this is a scandal that dwarfs Watergate — that his predecessor engaged in an illegal wiretap of his campaign. That is one potential scandal," Schiff said. "The alternative is a different kind of a scandal and that is a scandal of a sitting U.S. president alleging that his predecessor engaged in the most unscrupulous and unlawful conduct. That is also a scandal if those allegations prove to be false."

Nunes said his committee planned public hearings as part of its Russia probe, beginning with one on March 20 at which Federal Bureau of Investigation Director James Comey and Admiral Mike Rogers, director of the National Security Agency, were called to testify.

Former director of national intelligence James Clapper, former Central Intelligence Agency director John Brennan and former acting attorney general Sally Yates were also invited.

Nunes said the panel would not issue subpoenas for that hearing. "But if we have to, we will subpoena all information that is pertinent to this investigation if people ... don't want to appear or if the appropriate agencies do not provide the information we ask for."

Schiff addressed speculation that the issue was too partisan for Congress to conduct a credible investigation. "To be honest, we don't know yet. I can't say for certain that will be possible," he said at news briefing several hours after Nunes's.

With files from The Associated Press