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, a person familiar with the probe said Thursday.

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 and months. 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 use of a grand jury.

Grand juries are common vehicles to subpoena witnesses and records and to present evidence, though they do not suggest any criminal charges are near or will necessarily be sought. 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.

A spokesman for Mueller's team did not return an email seeking comment.

Mueller's reliance on a grand jury is the "logical next step in this investigation" given that it's the traditional method for prosecutors to gather evidence, said Washington defense lawyer Jacob Frenkel.

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."

It was not clear what witnesses might appear before the grand jury or what evidence it might be accumulating or presented with.

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 the city could be more convenient for the group of investigators than working out of Alexandria. Mueller also worked as a prosecutor in Washington before becoming FBI director, a job he held for 12 years.

A grand jury "increases the power of the prosecutors," said David Levine, law professor at the University of California Hastings College of Law. "Instead of asking for people to provide testimony, they can demand testimony under the penalty of perjury and under risk of contempt of court. And with respect to documents, instead of asking people for documents, they can demand documents. And so for example the tax returns, a subpoena can unlock those tax returns," he said.

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.

Under the regulations, Deputy Attorney General Rod Rosenstein is the government official empowered to fire Mueller under limited circumstances, such as conflict of interest and dereliction of duty. Rosenstein, who appointed Mueller, has publicly said he has seen no basis for firing him.

Oakland, California - Aug. 3, 2017

1. David Levine looks at news story on phone

2. Screen showing news story about grand jury in Russia probe

3. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

++ covered by video ++ "What we've learned is that special counsel Mueller and the lawyers working with him ++ are using a grand jury to further their investigation into the questions about Russian collusion and related areas such as financial transactions and other matters."

Washington, D.C. - June 21, 2017

4. AP Photo of former FBI director Robert Mueller arriving for meeting at Capitol Hill

Oakland, California - Aug. 3, 2017

5. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

++ covered by video ++ "It increases the power of the prosecutors. ++ Instead of asking for people to provide testimony, they can demand testimony under the penalty of perjury and under risk of contempt of court. And with respect to documents, instead of asking people for documents, they can demand documents. And so for example the tax returns, a subpoena can unlock those tax returns."

Huntington, West Virginia - Aug. 3, 2017

6. AP Photo of President Donald Trump speaking at rally

Washington, D.C. - Dec. 11, 1998

7. AP Photo of President Bill Clinton walking to Rose Garden to deliver statement on impeachment

Oakland, California - Aug. 3, 2017

8. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

++ covered by video ++ "If it's somebody in the United States, they are subject to subpoena. And that would include the president of the United States. Famously President Bill Clinton appeared before a grand jury. It turned out not very well for him."

Oakland, California - Aug. 3, 2017

9. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"We're probably months and months away before we hear formally ++ covered by video ++ from Mr. Mueller as to whether and who might be indicted and for what." ++

Washington, D.C. - June 21, 2017

10. AP Photo of former FBI director Robert Mueller arriving for meeting at Capitol Hill

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, a person familiar with the probe said Thursday.

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 and months. 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 use of a grand jury.

Grand juries are common vehicles to subpoena witnesses and records and to present evidence, though they do not suggest any criminal charges are near or will necessarily be sought. 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.

A spokesman for Mueller's team did not return an email seeking comment.

Mueller's reliance on a grand jury is the "logical next step in this investigation" given that it's the traditional method for prosecutors to gather evidence, said Washington defense lawyer Jacob Frenkel.

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."

It was not clear what witnesses might appear before the grand jury or what evidence it might be accumulating or presented with.

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 the city could be more convenient for the group of investigators than working out of Alexandria. Mueller also worked as a prosecutor in Washington before becoming FBI director, a job he held for 12 years.

A grand jury "increases the power of the prosecutors," said David Levine, law professor at the University of California Hastings College of Law. "Instead of asking for people to provide testimony, they can demand testimony under the penalty of perjury and under risk of contempt of court. And with respect to documents, instead of asking people for documents, they can demand documents. And so for example the tax returns, a subpoena can unlock those tax returns," he said.

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.

Under the regulations, Deputy Attorney General Rod Rosenstein is the government official empowered to fire Mueller under limited circumstances, such as conflict of interest and dereliction of duty. Rosenstein, who appointed Mueller, has publicly said he has seen no basis for firing him.

Oakland, California - Aug. 3, 2017

1. David Levine looks at news story on phone

2. Screen showing news story about grand jury in Russia probe

3. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"What we've learned is that special counsel Mueller and the lawyers working with him are using a grand jury to further their investigation into the questions about Russian collusion and related areas such as financial transactions and other matters."

Washington, D.C. - June 21, 2017

4. AP Photo of former FBI director Robert Mueller arriving for meeting at Capitol Hill

Oakland, California - Aug. 3, 2017

5. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"It increases the power of the prosecutors. Instead of asking for people to provide testimony, they can demand testimony under the penalty of perjury and under risk of contempt of court. And with respect to documents, instead of asking people for documents, they can demand documents. And so for example the tax returns, a subpoena can unlock those tax returns."

Huntington, West Virginia - Aug. 3, 2017

6. AP Photo of President Donald Trump speaking at rally

Oakland, California - Aug. 3, 2017

7. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"If it's somebody in the United States, they are subject to subpoena. And that would include the president of the United States. Famously President Bill Clinton appeared before a grand jury. It turned out not very well for him."

Washington, D.C. - Dec. 11, 1998

8. AP Photo of President Bill Clinton walking to Rose Garden to deliver statement on impeachment

Oakland, California - Aug. 3, 2017

9. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"If I was in the White House, I would be concerned that the investigation has gone up a notch or appears to have gone up another notch. In short order probably people who are in the administration or former members of the administration or former members of the campaign will be getting subpoenas to testify and provide documents."

Washington, D.C. - June 21, 2017

10. AP Photo of former FBI director Robert Mueller arriving for meeting at Capitol Hill

Oakland, California - Aug. 3, 2017

11. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"And as the word gets around in the White House as to who is getting subpoenas and what is being asked, at least some members of the administration will obviously be getting more more nervous. This is why so many of them already have - the parlance is they've lawyered up. So many of those senior officials each have their own lawyer or series of lawyers because of their concerns of where this may lead."

Huntington, West Virginia - Aug. 3, 2017

12. AP Photo of President Donald Trump speaking at rally

Oakland, California - Aug. 3, 2017

13. SOUNDBITE (English) David Levine, law professor, University of California, Hastings College of the Law

"We're probably months and months away before we hear formally from Mr. Mueller as to whether and who might be indicted and for what."

14. David Levine looking at phone