The White House has called for congressional committees probing Russian interference in the U.S. presidential election to also look at whether the Obama administration abused "executive branch investigative powers."
The statement comes a day after President Donald Trump alleged, without offering any evidence, that former President Barack Obama ordered a telephone tap on Trump during the campaign before last year's U.S. elections.
An aide to Obama said Trump's allegations were "simply false."
Trump did not cite any source for his claims, or provide any evidence that electronic surveillance occurred, but he likened the supposed intrusion on his privacy to the Watergate political scandal that eventually led to the 1974 resignation of former U.S. President Richard Nixon.
The scandal began as a series of political "dirty tricks" aimed at the Democratic Party by Nixon's Republicans, and it expanded after a White House official disclosed that Nixon had authorized an extensive monitoring operation at the White House, recording a large number of telephone calls.
No official in the White House during the Obama administration "ever interfered with any investigation led by the Justice Department," said Kevin Lewis, a spokesman for the former president, emphasizing that prohibition was a "cardinal rule."
In a statement, Lewis said neither "President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false."
VOA asked White House officials for a comment on Saturday's developments but did not receive an immediate response. Neither the FBI nor the Justice Department had any relevant statements.
FBI sought warrant
The Foreign Intelligence Surveillance Act of 1978 (FISA) permits legal surveillance and collection of information between foreign countries and their agents.
The FBI sought and was granted in October a FISA court warrant for an investigation into suspected ties between Russia and people connected to the Trump campaign, according to two sources and previous news reports.
The Justice Department believed four Americans were "unwitting agents" of Russia; there was "probable cause they had been co-opted, and that was the basis for the warrant" granted by the court, according to a lawyer specializing in national security matters, Bradley Moss, who spoke with VOA.
An earlier similar request by the FBI, wider in scope, apparently had been made to the secret court four months earlier, but was rejected. "That's largely unheard of," Moss said.
Search targeted contributions
The FBI and other federal investigators "follow the facts, and the assumption was this was about money … and that would have gone through Trump Tower," added Moss, who is also the deputy executive director of the James Madison Project, an organization focused on promoting government accountability and reduction of secrecy.
Ben Rhodes, a former top national security aide to Obama, said in a Twitter message directed at Trump on Saturday that "no president can order a wiretap," and added, "Those restrictions were put in place to protect citizens from people like you."
The highest-ranking Democrat on the Senate Foreign Relations Committee, Ben Cardin of Maryland, said if the Obama administration did monitor activities at Trump Tower, it would indeed have needed authorization from the FISA court.
"That's why we have the FISA courts," Cardin said Saturday on CNN. "The executive branch cannot act on its own. They must get the consent of a court before they can do those types of activities."
Graham 'very worried'
Republican Senator Lindsey Graham of South Carolina, a member of the Senate Judiciary Committee, did not endorse Trump's claims but said Saturday that if the Trump campaign was wiretapped in New York, "it would be the biggest political scandal since Watergate."
"I'm very worried that our president is suggesting that the former president has done something illegally," Graham added at a boisterous town hall meeting in Clemson, South Carolina. "I would be very worried if, in fact, the Obama administration was able to obtain a warrant, lawfully, about Trump campaign activity with foreign governments. So it's my job as a United States senator to get to the bottom of this."
It is unknown whether Obama was aware in advance that his Justice Department was pursuing FISA court approvals.
"I certainly expect he would have been advised" at some stage, Moss said.
Republican Senator Ben Sasse called Trump's allegations serious, and said if he was illegally tapped, the president should explain what sort of tap it was and how he knew about it.
Representative Adam Schiff, the senior Democrat on the House Intelligence Committee, said Trump was making "the most outlandish and destructive claims without providing a scintilla of evidence to support them."
Meetings with Russian ambassador
It was disclosed earlier this week that Russian Ambassador Sergei Kislyak met at Trump Tower in New York in December with Trump's son-in-law, Jared Kushner, and with since-ousted national security adviser Michael Flynn. Flynn was fired after just 24 days on the job when information emerged that he had lied to top officials about the nature of his conversations with Kislyak.
Revelations of the Trump Tower meetings surfaced after Attorney General Jeff Sessions admitted earlier in the week he'd met twice with Kislyak during last year's presidential campaign.
Sessions had failed to disclose those talks during his Senate confirmation hearing. He has since said he would stay out of any federal investigation of alleged Russian meddling in the 2016 presidential election and is expected to amend on Monday his written testimony response.
White House spokeswoman Hope Hicks said Thursday that the meetings at Trump Tower were intended to "establish a line of communication" between the incoming administration and the Russian ambassador. She added that Kushner also met with representatives of as many as two dozen other countries.
Investigations on the increase
U.S. government officials meet with representatives of foreign governments on many occasions and for many reasons. The Trump administration, however, had denied for months there was any contact between Russian officials and the new president's campaign.
On Friday, the Breitbart News website published a report about conservative radio host Mark Levin's allegation that Obama conducted what he called a "silent coup" against Trump by employing "police state" tactics. Trump's top strategic adviser at the White House, Stephen Bannon, previously had been executive chairman of Breitbart.
Trump's latest claims come as the Trump administration faces mounting pressure from multiple FBI and congressional investigations into contacts between members of his campaign team and Russian officials.
"I still don't know if there's any fire, but there's smoke here," national security lawyer Moss told VOA.