The governments of China, Russia and Iran are seeking to influence the forthcoming US elections, the country's top counterintelligence official says, warning that the Kremlin is already using a variety of measures to denigrate Democratic candidate Joe Biden.
In an unusual public statement, William Evanina, director of the National Counterintelligence and Security Centre, said the three countries were using online disinformation and other means to try to influence voters, stir up disorder and undermine American voters' confidence in the democratic process.
"Many foreign actors have a preference for who wins the election, which they express through a range of overt and private statements; covert influence efforts are rarer," Evanina said.
"We are primarily concerned about the ongoing and potential activity by China, Russia and Iran."
US President Donald Trump, asked at a news conference in New Jersey how he would respond to interference in the 3 November vote, said: "We're going to watch all of them, we have to be very careful."
Trump added that he believed Russia, China and Iran all wanted him to lose the election, repeating his claim that the biggest risk to the integrity of the election was mail-in ballots.
"It's much easier for [foreign countries] to forge ballots and send them in, it's much easier for them to cheat with universal mail-in ballots," he said.
"It would be difficult for our adversaries to interfere with or manipulate voting results at scale," Evanina said.
The latest intelligence assessment warned, however, that hostile foreign actors may seek to compromise election infrastructure, interfere with the voting process or call into question voting results.
The White House responded with a statement saying: "The United States will not tolerate foreign interference in our electoral processes and will respond to malicious foreign threats that target our democratic institutions."
The leaders of the Senate Intelligence Committee, Republican Marco Rubio and Democrat Mark Warner, thanked Evanina for his warning in a statement and added that all Americans "should endeavour to prevent outside actors from being able to interfere in our elections, influence our politics, and undermine confidence in our democratic institutions."
Biden already in the crosshairs of Russia
Evanina warned that Russia is already going after former vice-president Biden and what it regards as an anti-Russia US "establishment."
He said "Kremlin-linked actors" were trying to "boost President Trump's candidacy via social media and Russian television".
In a statement, the Biden campaign said Trump "publicly and repeatedly invited, emboldened, and even tried to coerce foreign interference in American elections."
Multiple reviews by US intelligence agencies have concluded that Russia acted to boost Trump's 2016 campaign and undercut his rival Hillary Clinton's chances in that election.
Trump has played down the findings, while the Russian government has denied claims of interference in US democracy.
Asked about the new intelligence assessment at a news conference, Trump seemed to disagree with the intelligence assessment that Russia was trying to denigrate Biden.
"I think the last person Russia wants to see in office is Donald Trump because nobody has been tougher on Russia than I have - ever," he said.
Tim Murtaugh, a spokesman for the Trump campaign, also insisted that Trump has been "tougher on Russia than any administration in history."
"We don't need or want foreign interference, and President Trump will beat Joe Biden fair and square," Murtaugh added.
Beijing and Tehran also believed to be meddling
US officials also believe that China does not want Trump to win a second term and has accelerated its criticism of the White House, expanding its efforts to shape public policy in America and to pressure political figures seen as opposed to Beijing's interests.
Trump expressed faith in this finding by officials, stating that: "If Joe Biden was president, China would own our country."
The Trump administration this week said it was effectively banning the popular Chinese-owned apps WeChat and TikTok in 45 days over national security concerns.
Evanina's statement, three months before the election, comes amid criticism from House Speaker Nancy Pelosi and other congressional Democrats that the intelligence community has been withholding from the public specific intelligence information about the threat of foreign interference in American politics.
On Iran, the assessment said Tehran seeks to undermine US democratic institutions as well as Trump and divide America before the election.
"Iran's efforts along these lines probably will focus on online influence, such as spreading disinformation on social media and recirculating anti-US content," Evanina wrote.
"Tehran's motivation to conduct such activities is, in part, driven by a perception that President Trump's re-election would result in a continuation of US pressure on Iran in an effort to foment regime change."
The findings were echoed by Cynthia Kaiser, the FBI's deputy chief of analysis for national cyber threats.
"If if you ask me what the biggest threat is, its the kind of constant drumbeat or influence campaigns that are going to make people feel like they are less confident in our [electoral] system," she said.