FBI director James Comey on Monday shot down President Donald Trump's tweeted claims that his predecessor Barack Obama had wiretapped the phones at Trump Tower in New York.
"With respect to the president's tweets about alleged wiretapping directed at him by the prior administration, I have no information that supports those tweets," Comey told a US congressional intelligence panel.
National Security Agency director Admiral Mike Rogers also strongly rebutted the suggestion, repeated by Trump's administration, that the NSA had asked Britain's GCHQ intelligence agency to spy on the US president.
"That would be expressly against the construct of the Five Eyes agreement that's been in place for decades," Rogers told the hearing, referring to the intelligence network grouping the United States, Britain, Australia, Canada and New Zealand.
The combined remarks were perhaps the strongest on-record repudiation yet by senior government officials of the president's extraordinary accusation against Obama.
Comey, speaking to a packed hearing of the House Intelligence Committee, said the lack of wiretapping evidence extended to the Department of Justice as well.
"The Department of Justice has asked me to share with you that the answer is the same for the Department of Justice and all its components," Comey told the panel.
Comey described the "rigorous" US statutory framework, which involves all three branches of government, under which courts grant permission for electronic surveillance.
Asked by the committee's top Democrat, Adam Schiff, whether Obama could have unilaterally ordered a wiretap of anyone, Comey responded: "No president could."
Trump created a firestorm early this month in a series of accusatory tweets.
"Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!" Trump tweeted.
Last Friday, he repeated his claim, rejecting rising calls from Republicans and Democrats to withdraw the charge and apologize.