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The U.S. government is gearing up for an unprecedented effort to protect Tuesday’s presidential election from cyber attack, U.S. officials told NBC News.

"There are a lot of eyes on this presidential election — more than there normally would be," a senior Obama administration official said.

Cyber centers at the Department of Homeland Security, the Justice Department and the FBI — as well as the Pentagon, the CIA and other intelligence agencies — will be on alert, with extra staff hunting for any possible threat, officials say.

The concern is so high, intelligence officials told NBC, that for the first time, hundreds of military and intelligence cyber experts who work out of top secret facilities, including underground bunkers, will be monitoring intelligence about a U.S. presidential election. They will react to any threat to the federal government's communication and command systems.

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"It’s all hands on deck," a senior intelligence official said.

U.S. officials have accused Russia of using cyber operations to meddle in the election, hacking into Democratic Party accounts and leaking the material to embarrass the Hillary Clinton campaign.

American officials are worried Russia will use its cyber capabilities to try to disrupt the presidential election itself, possibly by releasing fake documents and creating bogus social media accounts designed to spread misinformation.

"There is maybe a one in three chance of this happening but it's not insignificant."

On Tuesday, former NATO commander Admiral James Stavridis told CNBC his concerns about possible Russian activity included a dump of false documents and an attack on the U.S. power grid.

"There is maybe a one in three chance of this happening but it's not insignificant," said Stavridis.

On Friday the hacker known as "Guccifer 2.0" — which U.S. officials say is a front for Russian intelligence — tweeted a threat to monitor the U.S. elections "from inside the system."

U.S. officials have delivered a back channel warning to Russia not to do anything that would affect the vote. But there are widespread fears that cyber mischief by hackers, either from Russia or elsewhere, will somehow mar the election.

There are limits to what the U.S. government’s cyber force can do to protect American networks, most of which are owned by private companies. But the Pentagon’s cyber command has the capacity to retaliate in the event of a major attack on critical infrastructure.

"There is a whole-of-government effort in cyber around the election," a senior intelligence official said.