FBI chief James Comey on Monday said he had seen no evidence to substantiate a claim by US President Donald Trump that former president Barack Obama had wiretapped his 2016 election campaign.
Comey began his testimony to the US House of Representatives Intelligence Committee, Republican chairman Devin Nunes said it was possible other means of surveillance had been used against Trump.
The committee is investigating allegations that Russia tried to influence the 2016 election by hacking Democratic operatives and releasing embarrassing information.
The surveillance accusation became an issue when Trump earlier this month accused Obama of wiretapping Trump Tower in New York, which housed the campaign headquarters for the Republican's surprise election win against Democrat Hillary Clinton.
"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 the congressional hearing.
"And we have looked carefully inside the FBI. 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: the department has no information that supports those tweets," he said.
TRT World's Lorna Shaddick has more details from New York.
No physical wiretap
Comey also confirmed the agency is investigating possible Russian government efforts to interfere in the election, including any links between Trump's campaign and Moscow.
Russia denies it attempted to influence the November 8 presidential election.
Nunes had opened the hearing by denying Trump's wiretapping claim, but did not rule out other surveillance methods.
"We know there was not a physical wiretap of Trump Tower," he said. "However, it's still possible that other surveillance activities were used against President Trump and his associates."