Federal investigators have secured a warrant to examine newly discovered emails related to Hillary Clinton's private server, US media reports.
The warrant will allow the Federal Bureau of Investigation to examine the emails to see if they are relevant to its probe of the private email server used for government work by Ms Clinton, the Democratic presidential nominee, while she was secretary of state from 2009 to 2013.
FBI officials were unavailable for comment on the status of their investigation. Reuters could not independently confirm that the search warrant had been issued.
Mr Comey has come under heavy pressure from Democrats to quickly provide details of the emails, as Clinton allies worried the prolonged controversy could extend beyond the November 8 election and cast a shadow over a Clinton transition if she wins the White House.
US Senate Democratic leader Harry Reid sent a letter to Mr Comey on Sunday suggesting he violated the Hatch Act, which bars the use of a federal government position to influence an election.
"Through your partisan actions, you may have broken the law," Mr Reid, a senator from Nevada, said in the letter to Mr Comey.