Hillary Clinton attempted a serene demeanour on Monday just three days after FBI Director James Comey revealed investigators had uncovered a new trove of emails with a possible bearing on her use of a private server. “There is no case here,” she declared.

Speaking to supporters at Kent State University in Ohio, Ms Clinton said she had no problem with the FBI taking a look at the new emails predicting that when they were done they would reach the same conclusion they had in the first place - that nothing will warrant prosecution.

It was the first time Ms Clinton has directly addressed the issue in public since Mr Comey sent an electric shock through the race for president revealing in a brief letter to members of Congress the existence of the new emails and the intention to scrutinise them.

His announcement earned a furious reaction from many Democrats and others in Washington who variously accused Mr Comey either of trampling a long-held tradition of top officials avoiding doing anything that could influence an election in its final lap or actually of breaking the law while at the same time betraying his own bias in favour of the Republican, Donald Trump.

Not that Ms Clinton entirely hid her own irritation. “A lot of you may be asking what this new email story is about and why in the world the FBI would decide to jump into an election with no evidence of any wrong-doing with just days to go,” she declared. “That’s a good question.”

James Comey, FBI Director (Cliff Owen/AP)

But she otherwise played down the possible significance of the new FBI action, which has come about because of emails found on devices jointly owned by Huma Abedin, a trusted advisor and friend of Ms Clinton’s, and her husband, Anthony Weiner, who is quite separately under investigation for allegedly trading sexual messages with an under-age girl.

“As I have said, I am not making excuses. I have said it was a mistake and I regret it. And now they apparently want to look at emails of one of my staffers and by all means they should look at them and I am sure they will reach the same conclusion that they'd did when they looked at my e-mails this past year. There is no case here.”

The US Justice Department meanwhile reassured Congress that it would work as quickly as possible to resolve the latest questions about Ms Clinton's server. In a letter Monday, the department said it would work closely with the FBI and “take appropriate steps as expeditiously as possible.”

In London, the US Secretary of State admitted that the US election has at times become “downright embarrassing”, adding that without question it has sometimes veered “out of any norm”. He was talking to a group of sixth-form students in the British capital.

“The way it's made it difficult for me is that when you sit down with some foreign minister in another country, or with the president or prime minister of another country, and you say, 'Hey, we really want you to move more authoritatively towards democracy', they look at you ... they're polite, but you can see the question in their head and in their eyes," he confessed. "And in their expressions. It's hard."

While some senior Democrats, including Harry Reid, the Minority Leader in the US Senator, have lashed out at Mr Comey, a spokesman at the White House on Monday said that President Barack Obama was not of the opinion that the FBI Director was trying to influence the election.

President Obama believes that “Director Comey is a man of integrity,” Josh Earnest told reporters at the White House. “He's a man of principle and he's a man of good character.”

This was in direct contact to the fury voiced by Mr Reid who, in a letter penned to Mr Comey on Sunday, first said he may be guilty of breaking the Hatch Act which forbids federal officials from tampering with an election and second accused him of simultaneously sitting on information allegedly showing close ties and “coordination” between the Trump campaign and the Kremlin.

Meanwhile the former Attorney General, Eric Holder, wrote a column in the Washington Post openly criticising Mr Comey for carelessness.

"I fear he has unintentionally and negatively affected public trust in both the Justice Department and the FBI,“ Mr Holder wrote. "And he has allowed — again without improper motive — misinformation to be spread by partisans with less pure intentions.”

“That decision was incorrect. It violated long-standing Justice Department policies and tradition,“ added Mr Holder, who was also among a group of former senior Justice Department officials signing a joint letter similarly arguing that Mr Comey had committed a serious mistake.

As many as 20 million Americans have already made the choice for president either with early or absentee voting and it is hard to discern how large an impact the Comey grenade could have on the final result.

Polls this weekend showed some tightening of the polls in the final stretch before 8 November, but most of those surveys were conducted before Mr Comey revealed the existence of the new emails last Friday.