US Democratic presidential nominee Hillary Clinton acknowledges the crowd at a campaign rally in Cleveland, Ohio, US Nov 6, 2016. [Photo/Agencies]

WASHINGTON - The FBI said on Sunday it stood by its earlier finding that no criminal charges were warranted against Democrat Hillary Clinton for using a private email server for government work, lifting a cloud over her presidential campaign two days before the US election.

FBI Director James Comey made the announcement in a letter to Congress, saying the agency had worked "around the clock" to complete its review of newly discovered emails and found no reason to change its July finding.

"During that process, we reviewed all of the communications that were to or from Hillary Clinton while she was secretary of state," Comey said. "We have not changed our conclusions expressed in July."

A law enforcement source told Reuters the decision closes the FBI probe of Clinton's email practices.

Comey informed Congress of the newly discovered emails more than a week ago, throwing the race for the White House into turmoil and eroding Clinton's lead over Republican candidate Donald Trump in the final stretch before Tuesday's vote.

"We're glad this issue is resolved but for the record, this could easily have been learned before 1st letter was sent," Clinton spokesman Brian Fallon wrote on Twitter.

Republicans, however, did not ease up on their criticism of Clinton.

"She simply believes she's above the law and always plays by her own rules," House of Representatives Speaker Paul Ryan said in a statement, arguing that Clinton's use of a private email server "compromised our national security."

US stock index futures rose more than 1 percent after the FBI announcement, suggesting Wall Street is poised to end its longest skid in more than three decades. The US dollar also jumped in Asian trading against the yen, euro and Swiss franc.

Global financial markets last week slipped as polls showed the presidential race tightening.