Special counsel Robert Mueller said Wednesday he believed he was constitutionally barred from charging President Donald Trump with a crime but emphasized that his report did not exonerate the president.

The comments at an extraordinary press conference were Mueller’s first public statements since his appointment as special counsel two years ago.

“If we had had confidence that the president clearly did not commit a crime, we would have said so,” Mueller said. “We did not however make a determination as to whether the president did commit a crime.”

The statement came amid demands for Mueller to testify on Capitol Hill about his findings and tension with Attorney General William Barr.

Muller argued that his 448-page report spoke for itself.

"Beyond what I've said here today and what is contained in our written work, I do not believe it is appropriate for me to speak further," Mueller said in a brief press appearance at the Justice Department's headquarters.

He did not take questions.

Mueller said Justice Department policy prohibited him from bringing charges against a sitting president.

"Charging the president with a crime was ... not an option we could consider," Mueller told reporters as he announced his resignation from the Justice Department. "We concluded that we would not reach a determination one way or the other about whether the president committed a crime."

A redacted version of Mueller's report was published in April, concluding the campaign of President Donald Trump did not engage in a criminal conspiracy with Moscow to win the White House. Mueller declined to make a judgment on whether Trump obstructed justice, although the report outlined 10 instances in which Trump tried to impede the investigation.

Trump has said the two-year investigation exonerated him after repeatedly denouncing it as a witch hunt. The investigation ensnared dozens of people, including several top Trump advisers and a series of Russian nationals and companies.

Among them are his former campaign chairman, Paul Manafort, who is serving 7 1/2 years in prison for financial crimes and lobbying violations, and his former personal lawyer, Michael Cohen, who recently began a three-year sentence for campaign-finance violations and lying to Congress.

Since the report's release, Democratic lawmakers have tried without success to get the full report and underlying evidence. The House Judiciary Committee also is negotiating for Mueller to testify at a hearing.

Trump has said Mueller should not testify before Congress but that the final decision was up to Attorney General William Barr. Democrats have denounced Barr, saying he misrepresented the special counsel's findings.

Mueller appeared to have misgivings at one point as well, complaining to Barr in March that he had initially disclosed his main findings in an incomplete way that caused public confusion. In congressional testimony in April, Barr dismissed Mueller's concerns as "a bit snitty."

Barr now is leading a review of the origins of the Russia investigation in what is the third known inquiry into the FBI's handling of the matter. Trump harbors suspicions that the Democratic administration of President Barack Obama started the investigation in 2016 to undermine his presidency.