President Trump claims 'nasty and contentious' relationship with Mueller amounts to conflict of interest The president has brought up the unspecified claims of conflicts several times.

In a series of weekend tweets aimed directly at the special counsel Robert Mueller's Russia investigation, President Donald Trump accused Mueller of neglecting to report a series of unresolved conflicts including what he said was a previous "very nasty and contentious business relationship."

"Is Robert Mueller ever going to release his conflicts of interest with respect to President Trump," Trump tweeted Sunday afternoon. "Including the fact that we had a very nasty & contentious business relationship, I turned him down to head the FBI (one day before appointment as S.C.) & Comey is his close friend."

Asked about what specific conflict the president was referring to in a Monday interview with CNN, Trump's personal attorney Rudy Giuliani described it as a "dispute" but left it to the president to further characterize his complaint.

"He's referring to a dispute which I imagine Mueller -- I imagine he disclosed it to [Deputy Attorney General Rod] Rosenstein when he appointed him, because it would involve something that actually wasn't settled even to this day," Giuliani said. "That's up to the president and Mueller to describe, it's not part of my legal representation."

The president has previously raised questions regarding what he has alleged as conflicts of interest among Mueller's team dating back to as early as July 2017.

But so far, there haven’t been any known formal complaints raised by Trump's legal team as they insist they are still cooperating with Mueller's investigation.

The New York Times reported in January that Trump has cited a private dispute with Mueller over dues at Trump's golf club in Sterling, Va., as one potential conflict that would disqualify him serving as special counsel. The special counsel's spokesperson declined to comment in response to ABC News' questions regarding the president's allegations.

After Mueller's appointment in May 2017, the Department of Justice released a statement confirming that ethics experts reviewed his appointment and "determined that Mr. Mueller’s participation in the matters assigned to him is appropriate."

Additionally, in late June, Rosenstein was asked in front of Congress about the president's allegations that Mueller had a disqualifying conflict of interest.

"If there were any conflicts of interest that were brought to our attention, I would discuss with Mr. Mueller, and then there could be review within the department, if there were a credible allegation of a conflict of interest," Rosenstein answered. "And so I'm not aware of any disqualifying conflict of interest."

The president has also used his Twitter to allege partisan bias among Mueller's investigative team, which he has dubbed the "13 angry Democrats."

While 13 of the 17 investigators on Mueller's team have previously registered as Democrats with the other four not having publicly available details on their past political affiliations, Mueller himself is a registered Republican and was appointed by Rosenstein, who is also a Republican.

In testimony before Congress last December, Rosenstein personally defended Mueller's hiring decisions by noting that DOJ policy prohibits officials from asking about political affiliation when hiring for career positions.