Attorney-General William Barr says US intelligence agencies engaged in spying directed at the 2016 presidential campaign of Donald Trump and that he would look at whether the surveillance was undertaken legally.
"I think spying did occur," Barr told a Senate hearing on Wednesday.
"But the question is whether it was adequately predicated and I am not suggesting that it wasn't adequately predicated.... I am not suggesting those rules were violated, but I think it is important to look at that. And I am not talking about the FBI necessarily, but intelligence agencies more broadly.
"I think spying on a political campaign is a big deal - it's a big deal."
He later walked back the comment, calling it "unauthorised surveillance".
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Initially using language echoing Trump's attempts to discredit Special Counsel Robert Mueller's probe, Barr pulled back under questioning by Democratic senator Brian Schatz, who said the use of the term "spying" was "unnecessarily inflammatory".
Barr, a Trump appointee, said: "I want to make sure there was no unauthorised surveillance," modifying his language.
He said the Justice Department would release a redacted version of the Mueller report next week.
"I'm landing the plane right now," Barr said at a Senate appropriations committee hearing.
"I've been willing to discuss my letters and the process going forward, but the report is going to be out next week and I'm just not going to get details of the process until the plane's on the ground."
Barr discussed the report after a blistering assault by Trump on the FBI investigation that was taken over by Mueller, which the Republican President called an "attempted coup" involving "dirty cops".
Barr told the committee that he would review all the intelligence activities directed at Trump's 2016 campaign.
Barr noted much of this has been done already, both in congress and by the Justice Department inspector-general, but that he will pull it all together to see if there may be "remaining questions to be addressed".