In a stunning late night filing, the Department of Justice stated that neither the FBI nor its National Security Division wiretapped Trump Tower, contradicting a bombshell claim Trump made in a series of early morning tweets on March 4.
Democrats were upset that Nunes made the comments to the media and then briefed Trump in the White House without informing them.
The bureau monitored a Russian crime ring in the building from 2011 to 2013.
Rep. Devin Nunes said he obtained the information from a source he did not identify. Democrats said they had not been consulted about the information before the news conference.
FBI Director is expected to be asked about the president's surveillance assertions at a hearing Monday.
Trump made explosive accusations amid a Russia scandal in his administration.
Trump accused Obama of wiretapping him during the late stages of the campaign, but provided no evidence. Obama said through a spokesman that it was "simply false."
The president said that “wiretapping” covers “surveillance and many other things.”
Kellyanne Conway made the remarks to a New Jersey newspaper.
The House Intelligence Committee has set a Monday deadline for Justice to turn over any evidence it may have related to the president's accusations.
Republican Representative Devin Nunes told reporters that if Trump's assertion were true, leaders of Congress and the chairman of its two intelligence committees should have been briefed.
FBI head James Comey has asked the Justice Department to reject Trump's accusation that former President Barack Obama ordered a wiretap at Trump Tower.