Former FBI director James Comey testified before US lawmakers for the first time in over a year Friday, with much of the discussions centering on Hillary Clinton's email use.
The closed-door grilling came amid mounting intrigue over Special Counsel Robert Mueller's investigation into Russian interference in the 2016 election and possible contacts between Donald Trump's presidential campaign and Moscow.
Comey had pleaded for a public hearing after he was subpoenaed by the outgoing Congress in November, but House Republicans including some of Trump's allies insisted on a private session before the judiciary and oversight committees.
Comey was questioned as part of a Republican-led House inquiry into possible Russian interference, and Clinton, who lost to Trump in 2016, featured prominently.
"Hillary Clinton's emails, for heaven's sake," Comey said after testifying for six hours. "I'm not sure we need to do this at all."
Clinton had set up a private email server before becoming secretary of state in 2009.
Republicans seized on the revelation years later, saying she broke department protocol by using a private email account while a government official in order to hide sensitive correspondence.
The issue became a flashpoint of the 2016 race.
Republicans exited Friday's session complaining that Comey lawyers shut down certain avenues of questioning.
Comey disputed that but gave a rationale for why he would not publicly discuss some elements.
"The FBI, for understandable reasons, doesn't want me talking about the details of the investigation that is still ongoing, and began when I was FBI director," he said.
In May 2017 Trump abruptly sacked Comey, who was the senior official leading a criminal investigation into possible collusion with Moscow.
Three months earlier the president met privately with Comey and urged him to end the investigation into former national security advisor Michael Flynn, a move that many Democrats interpreted as obstruction of justice.
Trump has repeatedly blasted Mueller's probe as a "witch hunt," and on Friday unleashed a Twitter tirade against Mueller, Comey and other current and former officials tied to the Russia probe.
"Robert Mueller and Leakin' Lyin' James Comey are Best Friends, just one of many Mueller Conflicts of Interest," Trump tweeted.
Comey said a testimony transcript will be published 24 hours after his interview. Republicans want him to return for further testimony in two weeks, a final effort to advance their probe.
House control shifts to Democrats in January, and incoming Judiciary Committee chairman Jerrold Nadler said he would shut down the probe into FBI behaviour because it was merely an effort to "cast aspersion on the real investigation, which is Mueller."
James Comey was questioned as part of a Republican-led House inquiry into possible Russian interference, and Hillary Clinton, who lost to Trump in 2016, featured prominently.