LAS VEGAS — President Trump said Friday that the disclosure by American intelligence officials that Russia was again meddling in a presidential election in his favor was merely another partisan attack against him, continuing a pattern in which he has sought to dismiss warnings of foreign interference in American elections.

“Another misinformation campaign is being launched by Democrats in Congress saying that Russia prefers me to any of the Do Nothing Democrat candidates who still have been unable to, after two weeks, count their votes in Iowa,” Mr. Trump wrote on Twitter. “Hoax number 7!”

He was responding to reports of a classified briefing in which intelligence officials told members of the House Intelligence Committee that Russia was interfering in the 2020 presidential campaign to aid his re-election. Republicans on the committee challenged the conclusions and Mr. Trump berated Joseph Maguire, the outgoing acting director of national intelligence, for allowing the briefing to happen.

Intelligence officials have also concluded that the Russians are seeking to help Senator Bernie Sanders of Vermont in the Democratic presidential primaries.