(AP) - Special Counsel Robert Mueller is using a grand jury in Washington as part of an investigation into potential coordination between the Trump campaign and Russia, according to a person familiar with the probe.

The use of a grand jury, a standard prosecution tool in criminal investigations, suggests that Mueller and his team of investigators are likely to hear from witnesses and demand documents in the coming weeks. The person who confirmed to The Associated Press that Mueller had turned to a grand jury was not authorized to discuss the investigation by name and spoke on condition of anonymity.

The Wall Street Journal first reported the grand jury.

Grand juries are common vehicles to subpoena witnesses and records, though they do not suggest any criminal charges are near. It was not immediately clear how or whether the Washington grand jury was connected to the work of a separate one in Alexandria, Virginia. That panel has been used to gather information on Michael Flynn, Trump's former national security adviser.

Mueller was a former federal prosecutor in Washington before becoming FBI director, where he spent 12 years before stepping down in 2013.

Meanwhile, lawyers for President Donald Trump said they were unaware of the existence of a grand jury and had no information to suggest the president himself was under federal investigation.

"With respect to the news of the federal grand jury, I have no reason to believe that the president is under investigation," defense attorney John Dowd told the AP.

Ty Cobb, special counsel to the president, said he wasn't aware Mueller had started using a new grand jury.

"Grand jury matters are typically secret," Cobb said. "The White House favors anything that accelerates the conclusion of his work fairly. ... The White House is committed to fully cooperating with Mr. Mueller."

Mueller was appointed special counsel in May by the Justice Department following the firing by Trump of FBI Director James Comey.

He has since assembled a team of more than a dozen investigators, including current and former Justice Department prosecutors with experience in international bribery, organized crime and financial fraud. That team has been working at an undisclosed location in Washington, so presenting evidence inside a federal courthouse in Washington could be more convenient for the group of investigators than working out of Alexandria.

News of the grand jury came as senators introduced two bipartisan bills aimed at protecting Mueller from being fired by Trump, with both parties signaling resistance to any White House effort to derail the investigation into Russian meddling in last year's election.

Trump's defense team has been looking into potential conflicts of interest among members of Mueller's team, such as past political contributions to Democrats including Hillary Clinton, and Trump has warned that any effort by Mueller to look into his finances would fall outside the scope of Mueller's appointment.

Any firing of Mueller would have to be done by Deputy Attorney General Rod Rosenstein, who appointed Mueller and who has said he has seen no basis for dismissal.

Trump attorney Jay Sekulow told Fox News on Thursday that "the president is not thinking about firing Robert Mueller so the speculation that's out there is just incorrect."

He also downplayed the significance of the grand jury, calling it "a standard operating procedure when you've got a situation like this."