WASHINGTON — The U.S. government is geared up as never before to combat foreign election interference, but there are limits to what American intelligence agencies can do, even as determined adversaries build on their 2016 playbook, the nation's election security czar said Tuesday.

In prepared remarks before an elections group, and in an exclusive interview afterward with NBC News, Shelby Pierson, the election security threats executive at the Office of the Director of National Intelligence, said a number of adversaries may be poised to attempt election interference.

"The threats as we go into 2020 are more sophisticated," she said. "This is not a Russia-only problem. Russia, China, Iran, North Korea, non-state hacktivists all have opportunity, means and potentially motive to come after the United States in the 2020 election to accomplish their goals."

Pierson spoke at an election summit sponsored by the U.S. Election Assistance Commission, an independent, bipartisan agency that certifies voting systems and serves as a national clearinghouse of information on election administration.

Speaking to NBC News, Pierson said U.S. intelligence agencies are tracking hacking activity by Russia's military intelligence agencies, including efforts flagged Monday by a private security firm to gain access to networks at Burisma, the Ukrainian firm that employed Joe Biden's son.

Asked when the target of a hacking campaign might be notified, she said the intelligence community will provide information to candidates and parties that are judged to be the target of a leak or malign influence campaign by a foreign government if there is some way the targets can act on the information.

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"We are looking for detail and action-ability in the information — not just that we are cognizant of the activity but that what we can share is something that the target or the victim can act upon."

The government is constantly balancing whether to discuss intelligence gleaned from sensitive sources and methods, she said.

The Biden campaign would not comment on whether it had been notified.

Experts have long worried that, having influenced an election with leaks of genuine emails in 2016, the Russians may turn to doctored information in 2020. NBC News asked Pierson whether the government has a plan for that, and how intelligence agencies will sort out potential disinformation spread by foreign governments.

She said the government would do what it can, but "it's also important to recognize that the intelligence community doesn't always have the access and insights to know what's real and what's fake."

She also commented on the recent "NBC Nightly News" reporting by Cynthia McFadden and Kevin Monahan that some voting systems are still connecting to networks via modems. "We have judged that to be a vulnerability," she said, but added that the Department of Homeland Security would be better positioned to discuss the matter in detail.

Asked what is being done to deter the Russians, she said there were efforts underway to expose their actions, and secret intelligence operations designed to stop them.

She added, "I think it's important for us to keep messaging our adversaries that this activity will not be tolerated and there will be consequences."

Critics would point out that while some Trump administration officials have sent that message, the president himself has been accused of sending the opposite message — questioning the intelligence about Russian election interference, praising Russian president Vladimir Putin, and failing to publicly address the threat.

In December, Trump warned the Russian foreign minister "against any Russian attempts to interfere in United States elections," according to a White House readout of the meeting. How forceful the warning, and what language Trump used, was unclear.

"We're uniquely cognizant that as we share information on election threats, we don't want to undermine American confidence in our democratic process," Pierson said. "What I want for the American voting public is that they understand these threats, that they've heard about it so frequently that they have availed themselves of the resources to them, that they can know where to vote, know how to vote if they're not on the voter rolls, know where to seek authoritative information on candidates and ballot measures, so it's with the confidence of knowing these threats that they're empowered to participate in the process."

Pierson also commented on a recent NBC News investigation showing that voting systems in some counties connect to networks via modem, leaving them potentially open to hackers.