Mueller raised subpoena in meeting with Trump's lawyers

May 2 (UPI) -- Special Counsel Robert Mueller told attorneys for President Donald Trump at a meeting two months ago he could subpoena the commander in-chief to appear before a grand jury.

Trump's attorneys, who have been in active negotiations with Mueller's legal team over a potential interview, said the president had no obligation to talk with investigators regarding the Russia investigation, The Washington Post reported.

Citing two sources, ABC News reported Mueller, the leader of the Justice Department's Russia investigation, warned he could "compel" the president to testify if Trump declined to be interviewed.

In a series of tweets Wednesday, Trump said the Russia accusations are a "hoax," and there was "no obstruction of justice" when he fired former FBI Director James Comey last year.

The president said he's been focused on the duties of his office, such as "negotiations going on with North Korea over nuclear war, negotiations going on with China over trade deficits, Negotiations on NAFTA, and much more."

Trump also called the investigation a "sad chapter for law enforcement" and the system "rigged."

"At some point I will have no choice but to use the powers granted to the Presidency and get involved!" he added.

Last month, Trump added Rudolph Giuliani and two federal prosecutors -- Serene Raskin and Marty Raskin -- to his legal team.

Word over a potential subpoena was reported a day after The New York Times reported Trump's lawyers had created a list of 49 questions based off the ongoing negotiations with Justice Department investigators -- and centered on questions Mueller plans to ask the president.

The questions focus on events of the 2016 Trump campaign, transition and presidency -- and include Trump's firing of Comey, the Times report said.

Giuliani told the Post he is still considering possible conditions for the president before agreeing to an interview.

"Hopefully, we're getting near the end. We all on both sides have some important decisions to make," Giuliani said. "I still have a totally open mind on what the right strategy is, which we'll develop in the next few weeks."

Trump has repeatedly denied colluding with Russian agents before the 2016 vote, and has called the Justice Department probe a "witch hunt."