The comments by acting US Attorney Michael Sherwin appeared to be an effort to walk back claims that federal prosecutors in Arizona had made in a court filing late on Thursday, in which they claimed there was evidence that rioters intended "to capture and assassinate elected officials".

Sherwin said that his office is leading the prosecution effort but as local offices help to run down suspects in their districts, there may have been a "disconnect" on the evidence obtained so far in the cases.

Late on Thursday, federal prosecutors had made sweeping claims about the ongoing investigation in a filing as they asked a judge to detain Jacob Chansley, an Arizona man photographed wearing horns as he stood at the desk of Vice President Mike Pence in the chamber of the US Senate.

In the filing, they said Chansley left a note for Pence warning that "it's only a matter of time, justice is coming."

"Strong evidence, including Chansley's own words and actions at the Capitol, supports that the intent of the Capitol rioters was to capture and assassinate elected officials in the United States government," the memo said.

A spokeswoman for the US Attorney's Office in Arizona told Reuters the office plans to file an amended memo on Friday ahead of Chansley's appearance in federal court for his detention hearing.

At a press briefing on Friday, Sherwin said his office has brought 98 criminal prosecutions to date and has opened investigations into more than 275 people in connection with the Capitol riots.

Steven D'Antuono, Assistant Director in Charge of the FBI's Washington DC Field Office, urged suspects at the briefing to turn themselves in freely.

"To those of you who took part in the violence, here's something you should know: Every FBI field office in the country is looking for you," he said.

"As a matter of fact, even your friends and family are tipping us off."

Australian Associated Press