"To date, we have not seen fraud on a scale that could have effected a different outcome in the election," Barr told the Associated Press.
The comments are likely to infuriate President Trump and members of his legal team, who have increasingly turned their ire towards the Justice Department and FBI in recent days over the agencies' refusal to investigate baseless conspiracies of widespread voter fraud.
"You would think, if you're in the FBI or Department of Justice, this is -- this is the biggest thing you could be looking at," Trump said in a Sunday interview with Fox News host Maria Bartiromo. "Where are they? I have not seen anything. I mean, I just -- they just keep moving along, and they go on to the next president."
Barr specifically singled out one theory peddled by Trump and his allies that vote tabulation machines had been tampered with in a way to skew the election towards President-elect Joe Biden.
"There's been one assertion that would be systemic fraud and that would be the claim that machines were programmed essentially to skew the election results. And the DHS and DOJ have looked into that, and so far, we haven't seen anything to substantiate that," Barr said.
Separately, Barr appointed Connecticut U.S. Attorney John Durham as special counsel to investigate the origins of the investigation into Russian interference in the 2016 election. Durham was previously appointed to investigate any criminal wrongdoing in the way top leaders at the Justice Department and FBI handled the investigation, but Barr's decision to elevate him as a special counsel, done two weeks prior to the election, gives Durham an extra layer of protection -- he can't easily be fired in a Justice Department under a new administration.
"I decided the best thing to do would be to appoint them under the same regulation that covered Bob Muller, to provide Durham and his team some assurance that they'd be able to complete their work regardless of the outcome of the election," Barr told the AP on Tuesday.
Barr was seen arriving at the White House shortly after the interview was published but a spokesperson said it was for a "previously scheduled meeting" and not with the president. The attorney general left at about 5 p.m.
The Trump campaign immediately released a statement from President Trump's personal lawyer Rudy Giuliani and Trump campaign senior adviser Jenna Ellis saying Barr's "opinion appears to be without any knowledge or investigation of the substantial irregularities and evidence of systemic fraud."
They added, "With all due respect to the Attorney General, there hasn't been any semblance of a Department of Justice investigation."
In the days after Biden was officially projected as the winner of the election, Barr provoked outrage from current and former prosecutors when he issued a memo reversing longstanding DOJ policy intended to prevent announcements of election fraud investigations prior to states moving to certify their votes.
Barr said prosecutors were authorized "to pursue substantial allegations of voting and vote tabulation irregularities" in the event there are "clear and apparently-credible allegations of irregularities that, if true, could potentially impact the outcome of a federal election in an individual State."
At the same time, Barr urged investigators to be vigilant against "specious, speculative, fanciful or far-fetched claims" that he said "should not be a basis for initiating federal inquiries."
The memo led a top career official in the DOJ's elections crimes division to resign from his position, and a group of current federal prosecutors later sent a letter to Barr asking he rescind the policy reversal, calling it "not based in fact."
Sources close to Barr at the time who defended his decision to pen the memo described the elections policy as "antiquated," while saying that if no such investigation announcement was made as a result then it would, in the end, bolster arguments that the election was conducted securely and without massive fraud.
More than three weeks later, the DOJ and FBI have announced no such investigations relevant to the parameters of Barr's memo as an increasing number of states have moved forward with certifying their vote tabulations.
Barr told the AP that, to date, the department's investigations have been more isolated instances of potential fraud rather than anything indicating a systemic failure in how the election was carried out.
"Most claims of fraud are very particularized to a particular set of circumstances or actors or conduct," Barr said. "They are not systemic allegations and. And those have been run down; they are being run down," Barr said. "Some have been broad and potentially cover a few thousand votes. They have been followed up on."
Trump, who initially celebrated news of Barr's memo with a retweet, on Sunday went as far to suggest that the FBI and DOJ might be "involved" in an unspecified fraud conspiracy to elect Biden.
Republican Rep. Adam Kinzinger criticized the comment in a tweet accusing the president of peddling "baseless conspiracies."
"The @FBI did not rig the election," Kinzinger, of Illinois, said. "If you find yourself believing they did, please stop, and say it out loud, and you will realize how silly it sounds."https://twitter.com/RepKinzinger/status/1333162550431801344
Other Trump allies have expressed similar exasperation at the FBI's unwillingness to involve itself, amid their ongoing campaign to convince Republican electors that they should refuse to validate their state's votes over incremental allegations of fraud.
"I don't know where the FBI has been for the last three years," Trump attorney Rudy Giuliani said in a Nov. 19 news conference. "What do we have to do to get the FBI to wake up? Maybe we need a new agency to protect us."
Prior to his interview, Barr had gone more than a month without holding a public event and avoided giving any media interviews.
It was a notable contrast from his relatively frequent public appearances throughout the summer, including interviews where he repeatedly stoked conspiracies about foreign countries being able to flood the country with fraudulent mail-in ballots.
"This is playing with fire," Barr told CNN in a September interview. "We're very closely divided country here. And if people have to have confidence in the results of the election and the legitimacy of the government."
Barr's claim, however, was disputed by statements from top intelligence officials including the head of DHS' cyber division Christopher Krebs and National Counterintelligence and Security Center director William Evanina, who argued mail-in ballot systems were too complex for a foreign country to be able to successfully mount such a scheme. No evidence has thus far surfaced of any foreign countries successfully tampering with the election by mailing ballots into the U.S.
ABC News' Will Steakin contributed to this report.