Attorney General William Barr said no evidence of widespread voter fraud has been found that would change the result of the presidential election in the US.
The comments, from one of Donald Trump’s most ardent allies, come despite Mr Trump's repeated baseless claims that the election was stolen and his refusal to concede.
Mr Barr said US attorneys and FBI agents have been working to follow up specific complaints and information they had received but found no evidence that would change the vote’s outcome.
"To date, we have not seen fraud on a scale that could have effected a different outcome in the election," Mr Barr said.
Before the election, Mr Barr had repeatedly raised the notion that mail-in voter fraud could be especially vulnerable to fraud during the coronavirus pandemic as Americans feared going to polls.
Shortly after Mr Barr's statement was published, President Trump tweeted out more baseless claims of voter fraud.
And his attorney Rudy Giuliani and his campaign issued a scathing statement claiming that, "with all due respect to the Attorney General, there hasn't been any semblance" of an investigation.
Last month, Mr Barr issued a directive to US attorneys across the country allowing them to pursue any "substantial allegations" of voting irregularities, if they existed.
There was no evidence at that time of widespread fraud.
That memorandum gave prosecutors the ability to go around longstanding Justice Department policy that normally would prohibit such overt actions before the election was certified.
Soon after it was issued, the department's top elections crime official announced he would step aside from that position because of the memo.
The Trump campaign team led by Mr Giuliani has been alleging a widespread conspiracy by Democrats to dump millions of illegal votes into the system with no evidence.
They have filed multiple lawsuits in battleground states alleging that partisan poll watchers did not have a clear enough view at polling sites in some locations.
The claims have been repeatedly dismissed including by Republican judges who have ruled the suits lacked evidence.
Local Republicans in some battleground states have followed President Trump in making similar unsupported claims.
President Trump has railed against the election in tweets and in interviews though his own administration has said the 2020 election was the most secure ever.
President Trump recently allowed his administration to begin the transition over to Joe Biden, but has still refused to admit he lost.