The FBI should provide a "counterintelligence briefing" to all US lawmakers as Congress faces a foreign threat, House Speaker Nancy Pelosi, ranking Senate Democrat Chuck Schumer and the top Democrats on the House and Senate intelligence committees said in a letter published on Monday.

"We are gravely concerned, in particular, that Congress appears to be the target of a concerted foreign interference campaign, which seeks to launder and amplify disinformation in order to influence congressional activity, public debate, and the presidential election in November," they said.

Read more: Biden warns of 2020 US election interference from Russia and China

All four signatories have access to high-level intelligence. The letter, addressed to FBI chief Christopher Wray and dated July 13, did not specify which foreign governments or actors were believed to be behind the campaign. It also did not provide details on the campaign despite noting "the seriousness and specificity" of the threats.

However, the message also contained a confidential addendum whose content was not released to the public.

The politicians called on Wray's office to draft a plan for the briefing by the end of Monday.

US law enforcement agencies previously found evidence of Russian meddling in the 2016 election that saw President Donald Trump take office. Others have claimed China and Iran were also attempting to influence US public opinion, especially by pushing disinformation on social media

Last month, FBI director Wray said that China was trying to affect the 2020 US race through its constant effort to manipulate the US public.

"It's not an election-specific threat; it's really more of an all-year, all-the-time threat," he said. "But certainly that has implications for elections and they certainly have preferences that go along with that."

dj/nm (Reuters, AFP)