Special counsel utilizing DC grand jury in Russia investigation

The White House said it was unaware of the special counsel's action.

"Grand jury matters are typically secret," Cobb said in a statement.

"The White House favors anything that accelerates the conclusion of his work fairly ... The White House is committed to fully cooperating with Mr. Mueller," he added.

The source reached by ABC News said the Washington, D.C. grand jury has been used for week, after a panel in Alexandria, Virginia was similarly used to investigate matters tied to the Russia probe. The panel permits Mueller's team to subpoena materials, question witnesses under oath and potentially issue formal charges.

A spokesman for the special counsel's office declined to comment for this story.

"We have no reason to believe the president is under investigation here," said Sekulow.

"The president is not thinking about firing Bob Mueller," he said.

ABC News' Justin Fishel, Mike Levine, Jordyn Phelps, Geneva Sands and Trish Turner contributed to this report.

Editor’s note: This story has been updated to clarify that the source who spoke with ABC News said the grand jury being used by Mueller was already in existence.