Intelligence chiefs are planning a major operation to prevent Russian hackers from attacking next week's presidential election in an attempt to undermine US democracy.

Russian government-backed hackers have already been accused of targeting Hillary Clinton and passing data to WikiLeaks in an effort to scupper her presidential campaign.

The White House has ordered the Department of Homeland Security, the CIA, the National Security Agency and the Defence Department to prepare themselves for a possible cyber attack.

The Russian government under Vladimir Putin, pictured, is accused of hiring a team of internet hackers to to try and influence next week's election by undermining Democrat Hillary Clinton

The National Security Agency is currently monitoring the internet in an effort to thwart any targeted hacks before they have an opportunity to influence next week's election

Russia has already been accused of trying to influence the election by circulating faked letters deliberately designed to destroy Hillary Clinton's campaign for the White House

Officials have warned hackers may try and bring down power networks or even deliberately spread misinformation on the internet in an effort to subvert the electoral process.

Michael McFaul, former US ambassador to Moscow between 2012 and 2014 said: ' The Russians are in an offensive mode and [the U.S. is] working on strategies to respond to that, and at the highest levels.'

The FBI and U.S. intelligence agencies are already examining faked documents aimed at discrediting the Hillary Clinton campaign as part of a broader investigation into what US officials believe has been an attempt by Russia to disrupt the presidential election.

US Senator Tom Carper, a Democrat on the Senate Homeland Security Committee, has referred one of the documents to the FBI for investigation on the grounds that his name and stationery were forged to appear authentic.

In the letter identified as fake, Carper is quoted as writing to Clinton, 'We will not let you lose this election.'

The fake Carper letter, which was described to Reuters, is one of several documents presented to the Federal Bureau of Investigation and the US Department of Justice for review in recent weeks, the sources said.

A spokeswoman for Carper declined to comment.

Wikileaks chief Julian Assange has fuelled the election rigging conspiracy by claiming in a new interview that Mr Trump ‘won’t be permitted to win’ the election.

Mr Assange, who denies his anti-privacy website is being used by the Kremlin, offered no evidence for his startling claim.

As part of an investigation into suspected Russian hacking, FBI investigators have also asked Democratic Party officials to provide copies of other suspected faked documents that have been circulating along with emails and other legitimate documents taken in the hack, people involved in those conversations said.

The Russian hacking attempts are believed to be designed to bolster Trump's campaign

A spokesman for the FBI confirmed the agency was 'in receipt of a complaint about an alleged fake letter' related to the election but declined further comment. Others with knowledge of the matter said the FBI was also examining other fake documents that recently surfaced.

US intelligence officials have warned privately that a campaign they believe is backed by the Russian government to undermine the credibility of the US presidential election could move beyond the hacking of Democratic Party email systems. That could include posting fictional evidence of voter fraud or other disinformation in the run-up to voting on November 8, US officials have said.

Russian officials deny any such effort.

In addition to the Carper letter, the FBI has also reviewed a seven-page electronic document that carries the logos of Democratic pollster Joel Benenson's firm, the Benenson Strategy Group, and the Clinton Foundation, a person with knowledge of the matter said.

The document, identified as a fake by the Clinton campaign, claims poll ratings had plunged for Clinton and called for 'severe strategy changes for November' that could include 'staged civil unrest' and 'radiological attack' with dirty bombs to disrupt the vote.

Hillary Clinton, pictured here with Bernie Sanders has been forced to deal with the impact of thousands of confidential emails released by WikiLeaks as well as faked documentation

Like the Carper letter, it was not immediately clear where the fraudulent document had originated or how it had begun to circulate.

On October 20, Roger Stone, a former Trump aide and Republican operative, linked to a copy of the document on Twitter with the tag, 'If this is real: OMG!!'

Benenson's firm had no immediate comment. Craig Minassian, a spokesman for the Clinton Foundation, said the document was 'fake.' He said he did not know if the FBI had examined it.

Stone did not respond to emails requesting comment.

A spokesman for the Clinton campaign, Glen Caplin, said the document was a fake and part of a 'desperate stunt' to capitalize on the leak of Democratic emails by Wikileaks.

The developments highlight the unusually prominent role U.S. law enforcement and intelligence agencies have played in a contentious election and an ongoing debate about how public they can or should be about their inquiries.

FBI Director James Comey, a Republican appointed by President Obama, touched off an outcry from Democrats last week when he alerted Congress that agents had found other emails that could be linked to an inquiry into Clinton's use of a private email server when she was Secretary of State, effectively re-opening an investigation he had closed in July.

The White House believes Russian hackers want to 'sow confusion' among the electorate

One White House source told NBC News about Russian plans to 'sow as much confusion as possible and undermine our process in ways they've done elsewhere'.

He added: 'So this is to make sure that we have all the tools at our disposal and that we're prepared to respond to whatever it is that they do.

'We need to be prepared on every front, not just technical but messaging, and so on. Because any reporting irregularity could be incredibly disruptive. … They can cause tremendous chaos, and by the time we are able to attribute, the damage may have already been done.'

Officials were reluctant to discuss how they might be respond to such 'influence operations,' other than to say they will make efforts to counter misinformation and keep open communication nodes.

The U.S. intelligence community and the Department of Homeland Security assess that it would be extremely difficult for even a nation-state actor to alter actual ballot counts or election results by cyber-attack, a second senior administration official told NBC News.

VLADIMIR PUTIN DENIES ELECTION HACKING CLAIMS Vladimir Putin denied his government is trying to 'fix' the US election and accused Washington of trying to distract the public from the real issues. He rejected ' the hysteria about Russia's influence on the US presidential election'. Putin described the claims as 'mythical and fictitious'. He said: 'Does anyone seriously think Russia can somehow influence the American people's choice? 'Is America some kind of banana republic? America is a great power!' He also described claims that he wants Trump to triumph as 'sheer nonsense'. He added: 'It's just an instrument of political struggle, a way of manipulating public opinion. 'We don't know how Trump or Clinton will behave, what they will or will not deliver. We feel more or less indifferent about it. 'We will work with any president who will be elected by the American people.' Advertisement

'This assessment is based on the decentralized nature of our election system in this country and the number of protections state and local election officials have in place,' the official said. 'States ensure that voting machines are not connected to the Internet, and there are numerous checks and balances as well as extensive oversight at multiple levels built into our election process.'

However, a Department of Homeland Security official said, other possible hacks pose 'the potential for causing confusion and misperception' around the election.

For example, 'Somebody could tamper with voter registration information or unofficial election night reporting.'

While multiple intelligence officials told NBC that they have no specific warning about an Election Day attack, they also say they consider the massive and sophisticated internet disruption of Friday, Oct. 21, a potential dry run.

The 'distributed denial of service' attack on equipment provided by the company DYN, which took down popular internet sites like PayPal and Amazon for hours, 'had all the signs of what would be considered a drill,' said Ann Barron-DiCamillo, former director of Homeland Security's computer emergency readiness team.

If a similar attack began unfolding on Election Day, DHS would work with big internet providers such as Comcast (owner of NBC Universal) and Verizon to try to mitigate it, Barron-DiCamillo said. Since most of the internet is owned by private companies, the government relies on the private sector to help stop attacks, she said.

As is standard for major national events, all six federal cyber centers will be up and running, closely monitoring network traffic and hunting for malware.

'Given (the Russians') past behavior in other contexts, we understand the way they like to go about potentially causing confusion and so we want to make sure that we are mitigating that potential,' the DHS official said.

A current Obama administration national security official said that a White House working group has been watching Russia's apparent intervention in other foreign elections with growing concern.

A recent case study, the official said, was the October 16 parliamentary election in Montenegro.

The incumbent Democratic Party of Socialists narrowly won, but fell short of an absolute majority after facing stiff and well-financed opposition from a pro-Russian coalition that opposes the country's proposed membership in NATO — a position also held by Putin.

In the run-up to the election, US officials believe Russia secretly funneled money to opposition parties and either set up or co-opted friendly media outlets and 'influencers' to undermine the pro-West party and highlight the risks of joining NATO, the official said.

During the election, Russia launched a coordinated disinformation campaign using traditional and social media to allege widespread voting irregularities, including that dead people had been registered to vote, according to the Obama national security official. Social media networks were so bombarded with complaints and accusations that Montenegro ordered telecom operators to temporarily shut down WhatsApp, Viper and similar messaging apps, creating even more questions about the election, the official said.

A network of anti-censorship bloggers also reported that the website of Montenegro's top election observation NGO, the Center for Democratic Transitions (CDT), was knocked out for part of Election Day, raising concerns among U.S. officials about Russian interference.

Montenegro's state election commission released the final results October 29 — and certified the pro-NATO party's win — despite protests by the pro-Russian opposition party, which cited the very irregularities the US blames on Russia as reason to doubt the vote totals.

'It's the kind of thing that we are anticipating that they will try here,' the official said. 'But they will target whatever they can — voting infrastructure, putting out false stories about the Democratic Party intentionally manipulating the results. That's what they do.'

Montenegro's leaders publicly accused Russia of meddling in the election. Russian officials and opposition party members denied any interference, but Russia's foreign minister said NATO was being 'irresponsible' for supporting admission for Montenegro, which could come as soon as Spring 2017.