Washington (CNN) The House Intelligence Committee on Thursday issued subpoenas to two former Trump officials who pleaded guilty and cooperated in special counsel Robert Mueller's investigation.

The intelligence panel said it had subpoenaed former Trump campaign deputy Rick Gates and former national security adviser Michael Flynn . The pair pleaded guilty in the special counsel's probe before cooperating with the investigation, and their testimony is cited in Mueller's report.

House Intelligence Chairman Adam Schiff's decision to subpoena the Mueller witnesses signifies a new facet in the House Democrats' investigations into President Donald Trump, as it's the first subpoenas issued to targets of the Mueller probe.

The House Judiciary and Intelligence committees are operating on dual tracks in their examinations of the Mueller investigation: House Judiciary Chairman Jerry Nadler has issued subpoenas to former White House officials who figured prominently in the special counsel's obstruction investigation, while Schiff has now subpoenaed officials cited in the special counsel's investigation into Russian election interference.

"As part of our oversight work, the House Intelligence Committee is continuing to examine the deep counterintelligence concerns raised in Special Counsel Mueller's report, and that requires speaking directly with the fact witnesses," Schiff, a Democrat from California, said in a statement. "Both Michael Flynn and Rick Gates were critical witnesses for Special Counsel Mueller's investigation, but so far have refused to cooperate fully with Congress."