A defendant charged in connection with the Jan. 6 riots at the U.S. Capitol has been indicted on charges of conspiring with a second man to kill the FBI agents investigating him, the Department of Justice said on Friday.

Edward Kelley, the 33-year-old Jan. 6 defendant, and Austin Carter, 26, are both charged in a criminal complaint with conspiracy, retaliating against a federal official, solicitation of a crime of violence and making threats across state lines.

"Today's allegations that individuals sought to attack and hurt or kill FBI personnel are sickening. FBI employees honorably perform their duties protecting the American public and upholding the Constitution and they should be able to execute these duties without threats of violence," FBI Director Christopher Wray said in a written statement.

Both men were ordered detained during an initial court appearance on Friday in U.S. District Court in Knoxville, Tennessee.

Josh Hedrick, an attorney representing Carter, told Reuters in an email that "Mr. Carter maintains his innocence and we look forward to zealously defending him against these allegations." Kelley's attorney could not be reached for comment by Reuters on Friday evening.

Prosecutors say Kelley and Carter obtained a list of federal agents taking part in the investigation into Kelley and discussed plans to kill them with a cooperating witness. The cooperating witness was not identified in the court papers.

The two men are also accused of discussing with the cooperating witness a possible attack on the FBI's field office in Knoxville.

Kelley is among hundreds of defendants who have been charged in connection with the violent Jan. 6 protests at the U.S. Capitol as Congress met to certify President Joe Biden's 2020 election victory over incumbent Donald Trump.

He is charged with physically assaulting a U.S. Capitol police officer at the capitol and breaking a window of the building to gain entry. Kelley has pleaded not guilty to those charges.

(Reporting by Dan Whitcomb; Additional reporting by Tim Reid; Editing by Muralikumar Anantharaman and Michael Perry)