The comments came after US media reports that Mr Comey had urged against publicly accusing Russia of interfering in the US election, including alleged email hacking.
Mr Comey’s concern about releasing the information was due to the proximity to the election, reports say.
The FBI declined to comment to the BBC.
The statement that Mr Comey reportedly declined to sign off on was released by the Department of Homeland Security and the Office of the Director of National Intelligence on 7 October.
“The US intelligence community is confident that the Russian Government directed the recent compromises of emails from US persons and institutions, including from US political organisations… these thefts and disclosures are intended to interfere with the US election process,” it said.
There have been allegations that Russian hackers have targeted the Democrats in an effort to skew the election in favour of Donald Trump.
“It is impossible to view this as anything less than a blatant double standard,” Clinton campaign manager Robby Mook said. He also called on Mr Comey to “immediately explain this incongruence and apply the same standard to Donald Trump’s associates as he has applied to Hillary Clinton’s.”
Mr Comey has faced a fierce backlash for announcing on Friday, just 11 days before the presidential election, that the FBI is investigating new emails that may be linked to its probe into Mrs Clinton’s private email server.
It emerged in March 2015 that Mrs Clinton had been breaking federal rules by operating a private email server while she was secretary of state from 2009-13.
Her lawyers combed through the server and provided the State Department with 30,000 work-related emails, but her campaign deleted another 33,000 messages, saying they were personal in nature.
Mr Comey concluded in July that Mrs Clinton had been “extremely careless” in handling classified information, but there were no grounds for any charges.
But on Friday, he told Congress he had learned of fresh emails which might be “pertinent” to its previous inquiry and renewed the FBI probe.
The latest emails were found in a separate investigation into allegations that former congressman Anthony Weiner sent illicit text messages to a 15-year-old girl in North Carolina. Mr Weiner is married to one of Mrs Clinton’s closest aides, Huma Abedin.
The FBI has reportedly obtained a warrant to search the cache of emails belonging to Ms Abedin, which are believed to have been found on her estranged husband’s laptop.
