Jeff Sessions, U.S. attorney general, right, and Kirstjen Nielsen, U.S. secretary of Homeland Security (DHS).

U.S. intelligence officials say they're concerned about "ongoing campaigns" by Russia, China, Iran and other countries to undermine confidence in American democracy.

In a joint statement, the Office of the Director of National Intelligence, the Homeland Security Department, the Justice Department and the FBI say they're worried about activities that "seek to influence voter perceptions and decision-making" in the 2018 and 2020 elections.

The agencies say the "ongoing campaigns" could take many forms. Examples include attempts to influence voters through social media, sponsoring content in English language media such as the Russian outlet RT, or "seeding disinformation through sympathetic spokespersons regarding political candidates and disseminating foreign propaganda."

Intelligence officials said last year that Russia sought to influence the 2016 presidential election through similar means.