CNN —

       Former Republican House Speaker Newt Gingrich testified Thursday before a federal grand jury investigating January 6, 2021, according to a person familiar with the matter.

       Gingrich allegedly communicated with senior advisers to former President Donald Trump about television advertisements that relied on false claims of election fraud, according to documents obtained by the House select committee that investigated January 6. The panel also claimed Gingrich played a role in the effort to submit fake slates of electors in battleground states that Trump lost, according to committee documents.

       An attorney for Gingrich did not immediately respond to a request for comment.

       As the special counsel’s investigation into Trump’s retention of classified documents shows signs of wrapping up, the probe into the attack on the US Capitol and efforts to subvert the peaceful transfer of power following the 2020 election has carried on.

       Prosecutors have interviewed witnesses in recent weeks and, in at least one case with right-wing podcast host Steve Bannon, issued a new subpoena for grand jury testimony, people familiar with the matter said.

       This story has been updated with additional information.