President Donald Trump on Friday said he wouldn't prevent former special counsel Robert Mueller from testifying before Congress, telling reporters he would leave that decision up to Attorney General William Barr.

Barr said this week that he wouldn't prevent Mueller from testifying.

Talking to reporters alongside the prime minister of the Slovak Republic, Trump was asked whether he would "like to see Mueller testify."

"That's up to our attorney general, who I think has done a fantastic job," the president replied.

Barr, however, said during his testimony before the Senate Judiciary Committee on Wednesday that he wouldn't object to Mueller appearing.

"I've already said publicly I had no objection," Barr said Wednesday.

NBC News has reported that Democrats on the House Judiciary Committee have already made preparations to get Mueller to testify and that they were looking at May 15 as a possible date.

A source familiar with the situation told NBC News on Thursday that the committee was negotiating the possible testimony directly with Mueller's team, but that nothing had been finalized. Previously, the committee had been in discussions over Mueller's testimony with the Department of Justice.

Earlier Friday, before Trump's remarks, Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., sent a letter to Mueller offering him the opportunity to testify before the Senate panel about "any misrepresentation by the Attorney General of the substance" of a phone call between the attorney general and the special counsel about about Barr's four-page summary of the Mueller report and the resulting press coverage.

On Friday, Trump was also asked if he would prevent former White House counsel Don McGahn from testifying before Congress by invoking executive privilege. "That will all be determined over the next week or so," Trump said.

Mueller's nearly 450-page report detailed how McGahn had at least two phone calls with Trump in which the president "directed" him to contact Deputy Attorney General Rod Rosenstein to have Mueller "removed" — a key part of the special counsel's investigation into whether Trump obstructed justice.