Hillary Clinton's campaign has put pressure on FBI Director James Comey to release more details about the emails he says could be related to the investigation into her use of a private email server.

They demanded to know whether Mr Comey had even reviewed them himself.

Tim Kaine, Mrs Clinton's running mate, said Mr Comey owed it to the public to be more forthcoming about the emails under review by the FBI with only 10 days remaining before the election.

Mr Kaine's message aimed to counter Republican rival Donald Trump, who has seized on the reignited email controversy in hopes of sowing fresh doubts about Mrs Clinton's trustworthiness.

"As far as we know now, Director Comey knows nothing about the content of these emails. We don't know whether they're to or from Hillary at all," Mr Kaine said.

He said if Mr Comey "hasn't seen the emails, I mean they need to make that completely plain. Then they should work to see the emails and release the circumstances of those once they have done that analysis".

Mrs Clinton's campaign chairman, John Podesta, said Mr Comey's handling of the matter was "inappropriate" and urged him to be more transparent.

The FBI is looking into whether there was classified information on a device belonging to Anthony Weiner, the disgraced ex-congressman who is separated from long-time Clinton aide Huma Abedin.

Mr Comey, in a letter to Congress on Friday, said the FBI had recently come upon new emails while pursuing an unrelated case and was reviewing whether they were classified.

Mrs Clinton's team tried to make it cases on the Sunday news shows, joining Democratic leaders who have said it was "unprecedented" for such FBI action so close to an election.

Her campaign has called on Mr Comey to release all the facts known so far, and they have criticised his letter because, they contend, it lacks crucial details.

Mr Trump's campaign manager Kellyanne Conway said Mr Comey was in "an impossible spot" when he acknowledged the FBI was looking into the messages.

"Had he sat on the information, one can argue that he also would be interfering in the election," by failing to disclose the review, Ms Conway said.

Mrs Clinton said in Florida on Saturday that it was "pretty strange to put something like that out with such little information right before an election" and accused Mr Trump of using the issue to mislead voters in the final leg of the campaign.

But Mr Trump told a crowd in Golden, Colorado, on Saturday that the FBI's review of the email practices raises "everybody's deepest hope that justice, as last, can be properly delivered."

The controversy over Mrs Clinton's email practices while she served as secretary of State has dogged her for more than a year.

Four senior Democratic senators have urged the Justice Department and the FBI to provide more detailed information by Monday about what investigative steps are being taken, the number of emails involved and what is being done to determine how many of the emails are duplicative of those already reviewed by the FBI.

AP

In Fort Lauderdale, Florida, Mrs Clinton attended a service at a predominantly black church.

She did not mention the FBI inquiry but said scripture reminded them that "suffering produces endurance and endurance produces character and character produces hope".

Mr Trump visited a non denominational church in Las Vegas, where he swayed and clapped along to the music.

Later a law enforcement official told the Associated Press that FBI investigators in the Anthony Weiner sexting probe knew for weeks about the existence of the newly discovered emails that might be relevant to the Clinton email investigation.

Mr Comey said he was briefed on Thursday about that development and then told Congress on Friday that investigators had found emails that were potentially relevant to the Clinton investigation.

The emails were found on a device that belonged to Weiner, the estranged husband of close Clinton aide Huma Abedin.

AP