H.R. McMaster told reporters in a brief statement that The Washington Post report published Monday "is false" and "at no time" were intelligence sources or methods discussed during Trump's meeting with Russian Foreign Minister Sergey Lavrov.
The Post report says Trump revealed highly classified information about Islamic State militants to Lavrov and Russia's ambassador to the U.S., Sergey Kislyak, during a meeting at the White House last week.
McMaster says: "I was in the room. it didn't happen."
McMaster says the president did not discuss details that were not already known publicly.
The newspaper cited current and former U.S. officials who said Trump shared details about an Islamic State terror threat with Russian Foreign Minister Sergei Lavrov and Russian Ambassador Sergey Kislyak. The threat was related to the use of laptop computers on aircraft.
The White House denounced the report.
"This story is false. The president only discussed the common threats that both countries faced," said Dina Powell, deputy national security adviser for strategy, who attended the meeting.
National Security Adviser H.R. McMaster, who also participated in the meeting, downplayed the report as well.
"The president and the foreign minister reviewed common threats from terrorist organizations to include threats to aviation," McMaster said. "At no time were any intelligence sources or methods discussed and no military operations were disclosed that were not already known publicly."
The anonymous officials told the Post that the information Trump relayed during the May 10 meeting had been provided by a U.S. partner through an intelligence-sharing arrangement. They said it was considered so sensitive that details have been withheld from allies and tightly restricted even within the U.S. government.
The Post said the intelligence partner had not given the United States permission to share the material with Russian officials. By doing so, Trump jeopardized cooperation from an ally familiar with the inner workings of the Islamic State group.
Afterward, White House officials took steps to contain the damage, placing calls to the CIA and the National Security Agency, the newspaper said.
The CIA and the Office of the Director of National Intelligence declined to comment Monday evening.
It's unlikely that Trump has broken any law. As president, Trump has broad authority to declassify government secrets.
Lawmakers from both parties were quick to weigh in.
Sen. Bob Corker, R-Tenn., chairman of the Senate Foreign Relations Committee, told reporters Monday evening that the Trump White House "has got to do something soon to bring itself under control and order."
He said he would have more to say when he knows more about the news report.
"The shame of it is there's a really good national security team in place and there are good, productive things that are under way through them and through others," Corker said. "But the chaos that is being created by the lack of discipline - it's creating an environment that I think makes - it creates a worrisome environment."
The story prompted Sen. Martin Heinrich, D-N.M., to tweet: "Protip: Don't give the Russians classified information. #Classified101."
Sen. Mark Warner, D-Va., tweeted: "If true, this is a slap in the face to the intel community. Risking sources & methods is inexcusable, particularly with the Russians."