The New York Times, The Washington Post, and AP separately reported on February 20 that the warning was given during a closed-door briefing on February 13.
They cited two officials familiar with the briefing who asked for anonymity.
The Times said the briefing angered Trump, who said Democrats would use the information against him.
The U.S. intelligence community concluded that Russia meddled in the 2016 presidential election through social-media campaigns and the hacking of e-mails from Democratic accounts to boost Trump’s campaign and to hurt the chances of rival Hillary Clinton.
Trump has called the conclusions a “hoax” and has vehemently denied suggestions his team worked with Russian figures during the election. Russia has denied it interfered in the election.
The Times reported that, during the briefing, Trump’s allies challenged the intelligence officials’ warnings and said that the president had been tough on Russia.
At a public hearing this month, FBI Director Christopher Wray told the House of Representatives Judiciary Committee that Moscow was engaged in “information warfare” ahead of the November election through a covert social-media campaign to divide the public and sow discord.